[PATCH] mm: extend prefault helpers to fault in more than PAGE_SIZE
On Thu, Mar 1, 2012 at 20:22, Daniel Vetter wrote:
> +/* Multipage variants of the above prefault helpers, useful if more than
> + * PAGE_SIZE of date needs to be prefaulted. These are separate from the
> above
> + * functions (which only handle up to PAGE_SIZE) to avoid clobbering the
> + * filemap.c hotpaths. */
> +static inline int fault_in_multipages_writeable(char __user *uaddr, int size)
> +{
> + ? ? ? int ret;
> + ? ? ? const char __user *end = uaddr + size - 1;
Please drop the const.
> +
> + ? ? ? if (unlikely(size == 0))
> + ? ? ? ? ? ? ? return 0;
> +
> + ? ? ? /*
> + ? ? ? ?* Writing zeroes into userspace here is OK, because we know that if
> + ? ? ? ?* the zero gets there, we'll be overwriting it.
> + ? ? ? ?*/
> + ? ? ? while (uaddr <= end) {
> + ? ? ? ? ? ? ? ret = __put_user(0, uaddr);
> + ? ? ? ? ? ? ? if (ret != 0)
> + ? ? ? ? ? ? ? ? ? ? ? return ret;
> + ? ? ? ? ? ? ? uaddr += PAGE_SIZE;
> + ? ? ? }
> +
> + ? ? ? /* Check whether the range spilled into the next page. */
> + ? ? ? if (((unsigned long)uaddr & PAGE_MASK) ==
> + ? ? ? ? ? ? ? ? ? ? ? ((unsigned long)end & PAGE_MASK))
> + ? ? ? ? ? ? ? ret = __put_user(0, end);
include/linux/pagemap.h:483:3: error: read-only location '*end' used
as 'asm' output
Now in -next:
http://kisskb.ellerman.id.au/kisskb/buildresult/6100650/
http://kisskb.ellerman.id.au/kisskb/buildresult/6100673/
http://kisskb.ellerman.id.au/kisskb/buildresult/6100860/
Gr{oetje,eeting}s,
? ? ? ? ? ? ? ? ? ? ? ? Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at
linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
? ? ? ? ? ? ? ? ? ? ? ? ? ?? ?? -- Linus Torvalds
Re: [PATCH] mm: extend prefault helpers to fault in more than PAGE_SIZE
On Thu, Mar 1, 2012 at 20:22, Daniel Vetter daniel.vet...@ffwll.ch wrote:
+/* Multipage variants of the above prefault helpers, useful if more than
+ * PAGE_SIZE of date needs to be prefaulted. These are separate from the
above
+ * functions (which only handle up to PAGE_SIZE) to avoid clobbering the
+ * filemap.c hotpaths. */
+static inline int fault_in_multipages_writeable(char __user *uaddr, int size)
+{
+ int ret;
+ const char __user *end = uaddr + size - 1;
Please drop the const.
+
+ if (unlikely(size == 0))
+ return 0;
+
+ /*
+ * Writing zeroes into userspace here is OK, because we know that if
+ * the zero gets there, we'll be overwriting it.
+ */
+ while (uaddr = end) {
+ ret = __put_user(0, uaddr);
+ if (ret != 0)
+ return ret;
+ uaddr += PAGE_SIZE;
+ }
+
+ /* Check whether the range spilled into the next page. */
+ if (((unsigned long)uaddr PAGE_MASK) ==
+ ((unsigned long)end PAGE_MASK))
+ ret = __put_user(0, end);
include/linux/pagemap.h:483:3: error: read-only location '*end' used
as 'asm' output
Now in -next:
http://kisskb.ellerman.id.au/kisskb/buildresult/6100650/
http://kisskb.ellerman.id.au/kisskb/buildresult/6100673/
http://kisskb.ellerman.id.au/kisskb/buildresult/6100860/
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- ge...@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say programmer or something like that.
-- Linus Torvalds
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[PATCH] mm: extend prefault helpers to fault in more than PAGE_SIZE
On Thu, Mar 01, 2012 at 12:15:57PM -0800, Andrew Morton wrote: > On Thu, 1 Mar 2012 20:22:59 +0100 > Daniel Vetter wrote: > > > drm/i915 wants to read/write more than one page in its fastpath > > and hence needs to prefault more than PAGE_SIZE bytes. > > > > Add new functions in filemap.h to make that possible. > > > > Also kill a copy spurious space in both functions while at it. > > > > > > ... > > > > +/* Multipage variants of the above prefault helpers, useful if more than > > + * PAGE_SIZE of date needs to be prefaulted. These are separate from the > > above > > + * functions (which only handle up to PAGE_SIZE) to avoid clobbering the > > + * filemap.c hotpaths. */ > > Like this please: > > /* > * Multipage variants of the above prefault helpers, useful if more than > * PAGE_SIZE of date needs to be prefaulted. These are separate from the above > * functions (which only handle up to PAGE_SIZE) to avoid clobbering the > * filemap.c hotpaths. > */ > > and s/date/data/ ... > Please merge it via the DRI tree. Ok, I've queued this up 3.5 (it missed the 3.4 merge because a few of the drm/i915 patches from that series haven't been reviewed in time) with the comment fixed up and your Acked-by on the commit message. I hope the later is ok, otherwise please yell. Thanks for reviewing this. -Daniel -- Daniel Vetter Mail: daniel at ffwll.ch Mobile: +41 (0)79 365 57 48
[PATCH] mm: extend prefault helpers to fault in more than PAGE_SIZE
drm/i915 wants to read/write more than one page in its fastpath
and hence needs to prefault more than PAGE_SIZE bytes.
Add new functions in filemap.h to make that possible.
Also kill a copy spurious space in both functions while at it.
v2: As suggested by Andrew Morton, add a multipage parameter to both
functions to avoid the additional branch for the pagemap.c hotpath.
My gcc 4.6 here seems to dtrt and indeed reap these branches where not
needed.
v3: Becaus I couldn't find a way around adding a uaddr += PAGE_SIZE to
the filemap.c hotpaths (that the compiler couldn't remove again),
let's go with separate new functions for the multipage use-case.
Cc: linux-mm at kvack.org
Signed-off-by: Daniel Vetter
---
drivers/gpu/drm/i915/i915_gem.c|6 +-
drivers/gpu/drm/i915/i915_gem_execbuffer.c |2 +-
include/linux/pagemap.h| 62 +++-
3 files changed, 64 insertions(+), 6 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 544e528..3e631fc 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -436,7 +436,7 @@ i915_gem_shmem_pread(struct drm_device *dev,
mutex_unlock(>struct_mutex);
if (!prefaulted) {
- ret = fault_in_pages_writeable(user_data, remain);
+ ret = fault_in_multipages_writeable(user_data, remain);
/* Userspace is tricking us, but we've already clobbered
* its pages with the prefault and promised to write the
* data up to the first fault. Hence ignore any errors
@@ -822,8 +822,8 @@ i915_gem_pwrite_ioctl(struct drm_device *dev, void *data,
args->size))
return -EFAULT;
- ret = fault_in_pages_readable((char __user *)(uintptr_t)args->data_ptr,
- args->size);
+ ret = fault_in_multipages_readable((char __user
*)(uintptr_t)args->data_ptr,
+ args->size);
if (ret)
return -EFAULT;
diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index 81687af..ef87f52 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -955,7 +955,7 @@ validate_exec_list(struct drm_i915_gem_exec_object2 *exec,
if (!access_ok(VERIFY_WRITE, ptr, length))
return -EFAULT;
- if (fault_in_pages_readable(ptr, length))
+ if (fault_in_multipages_readable(ptr, length))
return -EFAULT;
}
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index cfaaa69..0a91375 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -426,7 +426,7 @@ static inline int fault_in_pages_writeable(char __user
*uaddr, int size)
*/
if (((unsigned long)uaddr & PAGE_MASK) !=
((unsigned long)end & PAGE_MASK))
- ret = __put_user(0, end);
+ ret = __put_user(0, end);
}
return ret;
}
@@ -445,13 +445,71 @@ static inline int fault_in_pages_readable(const char
__user *uaddr, int size)
if (((unsigned long)uaddr & PAGE_MASK) !=
((unsigned long)end & PAGE_MASK)) {
- ret = __get_user(c, end);
+ ret = __get_user(c, end);
(void)c;
}
}
return ret;
}
+/* Multipage variants of the above prefault helpers, useful if more than
+ * PAGE_SIZE of date needs to be prefaulted. These are separate from the above
+ * functions (which only handle up to PAGE_SIZE) to avoid clobbering the
+ * filemap.c hotpaths. */
+static inline int fault_in_multipages_writeable(char __user *uaddr, int size)
+{
+ int ret;
+ const char __user *end = uaddr + size - 1;
+
+ if (unlikely(size == 0))
+ return 0;
+
+ /*
+* Writing zeroes into userspace here is OK, because we know that if
+* the zero gets there, we'll be overwriting it.
+*/
+ while (uaddr <= end) {
+ ret = __put_user(0, uaddr);
+ if (ret != 0)
+ return ret;
+ uaddr += PAGE_SIZE;
+ }
+
+ /* Check whether the range spilled into the next page. */
+ if (((unsigned long)uaddr & PAGE_MASK) ==
+ ((unsigned long)end & PAGE_MASK))
+ ret = __put_user(0, end);
+
+ return ret;
+}
+
+static inline int fault_in_multipages_readable(const char __user *uaddr,
+ int size)
+{
+ volatile char c;
+ int ret;
+ const char __user *end = uaddr + size - 1;
+
+ if (unlikely(size == 0))
+
[PATCH] mm: extend prefault helpers to fault in more than PAGE_SIZE
On Thu, 1 Mar 2012 20:22:59 +0100
Daniel Vetter wrote:
> drm/i915 wants to read/write more than one page in its fastpath
> and hence needs to prefault more than PAGE_SIZE bytes.
>
> Add new functions in filemap.h to make that possible.
>
> Also kill a copy spurious space in both functions while at it.
>
>
> ...
>
> +/* Multipage variants of the above prefault helpers, useful if more than
> + * PAGE_SIZE of date needs to be prefaulted. These are separate from the
> above
> + * functions (which only handle up to PAGE_SIZE) to avoid clobbering the
> + * filemap.c hotpaths. */
Like this please:
/*
* Multipage variants of the above prefault helpers, useful if more than
* PAGE_SIZE of date needs to be prefaulted. These are separate from the above
* functions (which only handle up to PAGE_SIZE) to avoid clobbering the
* filemap.c hotpaths.
*/
and s/date/data/
> +static inline int fault_in_multipages_writeable(char __user *uaddr, int size)
> +{
> + int ret;
> + const char __user *end = uaddr + size - 1;
> +
> + if (unlikely(size == 0))
> + return 0;
> +
> + /*
> + * Writing zeroes into userspace here is OK, because we know that if
> + * the zero gets there, we'll be overwriting it.
> + */
Yeah, like that.
> + while (uaddr <= end) {
> + ret = __put_user(0, uaddr);
> + if (ret != 0)
> + return ret;
> + uaddr += PAGE_SIZE;
> + }
> +
> + /* Check whether the range spilled into the next page. */
> + if (((unsigned long)uaddr & PAGE_MASK) ==
> + ((unsigned long)end & PAGE_MASK))
> + ret = __put_user(0, end);
> +
> + return ret;
> +}
> +
> +static inline int fault_in_multipages_readable(const char __user *uaddr,
> +int size)
> +{
> + volatile char c;
> + int ret;
> + const char __user *end = uaddr + size - 1;
> +
> + if (unlikely(size == 0))
> + return 0;
> +
> + while (uaddr <= end) {
> + ret = __get_user(c, uaddr);
> + if (ret != 0)
> + return ret;
> + uaddr += PAGE_SIZE;
> + }
> +
> + /* Check whether the range spilled into the next page. */
> + if (((unsigned long)uaddr & PAGE_MASK) ==
> + ((unsigned long)end & PAGE_MASK)) {
> + ret = __get_user(c, end);
> + (void)c;
> + }
> +
> + return ret;
> +}
Please merge it via the DRI tree.
[PATCH] mm: extend prefault helpers to fault in more than PAGE_SIZE
On Wed, Feb 29, 2012 at 03:01:46PM -0800, Andrew Morton wrote:
> On Wed, 29 Feb 2012 15:03:31 +0100
> Daniel Vetter wrote:
>
> > drm/i915 wants to read/write more than one page in its fastpath
> > and hence needs to prefault more than PAGE_SIZE bytes.
> >
> > I've checked the callsites and they all already clamp size when
> > calling fault_in_pages_* to the same as for the subsequent
> > __copy_to|from_user and hence don't rely on the implicit clamping
> > to PAGE_SIZE.
> >
> > Also kill a copy spurious space in both functions while at it.
> >
> > v2: As suggested by Andrew Morton, add a multipage parameter to both
> > functions to avoid the additional branch for the pagemap.c hotpath.
> > My gcc 4.6 here seems to dtrt and indeed reap these branches where not
> > needed.
> >
>
> I don't think this produced a very good result :(
And I halfway expected this mail here ;-)
> > ...
> >
> > -static inline int fault_in_pages_writeable(char __user *uaddr, int size)
> > +static inline int fault_in_pages_writeable(char __user *uaddr, int size,
> > + bool multipage)
> > {
> > int ret;
> > + char __user *end = uaddr + size - 1;
> >
> > if (unlikely(size == 0))
> > return 0;
> > @@ -416,36 +419,46 @@ static inline int fault_in_pages_writeable(char
> > __user *uaddr, int size)
> > * Writing zeroes into userspace here is OK, because we know that if
> > * the zero gets there, we'll be overwriting it.
> > */
> > - ret = __put_user(0, uaddr);
> > - if (ret == 0) {
> > - char __user *end = uaddr + size - 1;
> > + do {
> > + ret = __put_user(0, uaddr);
> > + if (ret != 0)
> > + return ret;
> > + uaddr += PAGE_SIZE;
> > + } while (multipage && uaddr <= end);
> >
> > + if (ret == 0) {
> > /*
> > * If the page was already mapped, this will get a cache miss
> > * for sure, so try to avoid doing it.
> > */
> > - if (((unsigned long)uaddr & PAGE_MASK) !=
> > + if (((unsigned long)uaddr & PAGE_MASK) ==
> > ((unsigned long)end & PAGE_MASK))
> > - ret = __put_user(0, end);
> > + ret = __put_user(0, end);
> > }
> > return ret;
> > }
>
> One effect of this change for the filemap.c callsite is that `uaddr'
> now gets incremented by PAGE_SIZE. That happens to not break anything
> because we then mask `uaddr' with PAGE_MASK, and if gcc were really
> smart, it could remove that addition. But it's a bit ugly.
Yep, gcc is not clever enough to reap the addl on uaddr (and change the
check for 'do we need to fault the 2nd page to' from jne to je again).
I've checked that before submitting - maybe should have mentioned this.
> Ideally the patch would have no effect upon filemap.o size, but with an
> allmodconfig config I'm seeing
>
>textdata bss dec hex filename
> 22876 1187344 303387682 mm/filemap.o (before)
> 22925 1187392 3043576e3 mm/filemap.o (after)
>
> so we are adding read()/write() overhead, and bss mysteriously got larger.
>
> Can we improve on this? Even if it's some dumb
>
> static inline int fault_in_pages_writeable(char __user *uaddr, int size,
> bool multipage)
> {
> if (multipage) {
> do-this
> } else {
> do-that
> }
> }
>
> the code duplication between do-this and do-that is regrettable, but at
> least it's all in the same place in the same file, so we won't
> accidentally introduce skew later on.
>
> Alternatively, add a separate fault_in_multi_pages_writeable() to
> pagemap.h. I have a bad feeling this is what your original patch did!
>
> (But we *should* be able to make this work! Why did this version of
> the patch go so wrong?)
Well, I couldn't reconcile the non-multipage with the multipage versions
of these functions - at least not without changing them slightly (like
this patch here does). Which is why I've asked you whether I should just
add a new multipage version of these. I personally deem your proposal of
using and if (multipage) with no shared code too ugly. But you've shot at
it a bit, so I've figured that this version here is what you want.
I'll redo this patch by adding _multipage versions of these 2 functions
for i915.
Yours, Daniel
--
Daniel Vetter
Mail: daniel at ffwll.ch
Mobile: +41 (0)79 365 57 48
[PATCH] mm: extend prefault helpers to fault in more than PAGE_SIZE
drm/i915 wants to read/write more than one page in its fastpath
and hence needs to prefault more than PAGE_SIZE bytes.
Add new functions in filemap.h to make that possible.
Also kill a copypasted spurious space in both functions while at it.
v2: As suggested by Andrew Morton, add a multipage parameter to both
functions to avoid the additional branch for the pagemap.c hotpath.
My gcc 4.6 here seems to dtrt and indeed reap these branches where not
needed.
v3: Becaus I couldn't find a way around adding a uaddr += PAGE_SIZE to
the filemap.c hotpaths (that the compiler couldn't remove again),
let's go with separate new functions for the multipage use-case.
Cc: linux...@kvack.org
Signed-off-by: Daniel Vetter daniel.vet...@ffwll.ch
---
drivers/gpu/drm/i915/i915_gem.c|6 +-
drivers/gpu/drm/i915/i915_gem_execbuffer.c |2 +-
include/linux/pagemap.h| 62 +++-
3 files changed, 64 insertions(+), 6 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 544e528..3e631fc 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -436,7 +436,7 @@ i915_gem_shmem_pread(struct drm_device *dev,
mutex_unlock(dev-struct_mutex);
if (!prefaulted) {
- ret = fault_in_pages_writeable(user_data, remain);
+ ret = fault_in_multipages_writeable(user_data, remain);
/* Userspace is tricking us, but we've already clobbered
* its pages with the prefault and promised to write the
* data up to the first fault. Hence ignore any errors
@@ -822,8 +822,8 @@ i915_gem_pwrite_ioctl(struct drm_device *dev, void *data,
args-size))
return -EFAULT;
- ret = fault_in_pages_readable((char __user *)(uintptr_t)args-data_ptr,
- args-size);
+ ret = fault_in_multipages_readable((char __user
*)(uintptr_t)args-data_ptr,
+ args-size);
if (ret)
return -EFAULT;
diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index 81687af..ef87f52 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -955,7 +955,7 @@ validate_exec_list(struct drm_i915_gem_exec_object2 *exec,
if (!access_ok(VERIFY_WRITE, ptr, length))
return -EFAULT;
- if (fault_in_pages_readable(ptr, length))
+ if (fault_in_multipages_readable(ptr, length))
return -EFAULT;
}
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index cfaaa69..0a91375 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -426,7 +426,7 @@ static inline int fault_in_pages_writeable(char __user
*uaddr, int size)
*/
if (((unsigned long)uaddr PAGE_MASK) !=
((unsigned long)end PAGE_MASK))
- ret = __put_user(0, end);
+ ret = __put_user(0, end);
}
return ret;
}
@@ -445,13 +445,71 @@ static inline int fault_in_pages_readable(const char
__user *uaddr, int size)
if (((unsigned long)uaddr PAGE_MASK) !=
((unsigned long)end PAGE_MASK)) {
- ret = __get_user(c, end);
+ ret = __get_user(c, end);
(void)c;
}
}
return ret;
}
+/* Multipage variants of the above prefault helpers, useful if more than
+ * PAGE_SIZE of date needs to be prefaulted. These are separate from the above
+ * functions (which only handle up to PAGE_SIZE) to avoid clobbering the
+ * filemap.c hotpaths. */
+static inline int fault_in_multipages_writeable(char __user *uaddr, int size)
+{
+ int ret;
+ const char __user *end = uaddr + size - 1;
+
+ if (unlikely(size == 0))
+ return 0;
+
+ /*
+* Writing zeroes into userspace here is OK, because we know that if
+* the zero gets there, we'll be overwriting it.
+*/
+ while (uaddr = end) {
+ ret = __put_user(0, uaddr);
+ if (ret != 0)
+ return ret;
+ uaddr += PAGE_SIZE;
+ }
+
+ /* Check whether the range spilled into the next page. */
+ if (((unsigned long)uaddr PAGE_MASK) ==
+ ((unsigned long)end PAGE_MASK))
+ ret = __put_user(0, end);
+
+ return ret;
+}
+
+static inline int fault_in_multipages_readable(const char __user *uaddr,
+ int size)
+{
+ volatile char c;
+ int ret;
+ const char __user *end = uaddr + size - 1;
+
+ if
Re: [PATCH] mm: extend prefault helpers to fault in more than PAGE_SIZE
On Thu, 1 Mar 2012 20:22:59 +0100
Daniel Vetter daniel.vet...@ffwll.ch wrote:
drm/i915 wants to read/write more than one page in its fastpath
and hence needs to prefault more than PAGE_SIZE bytes.
Add new functions in filemap.h to make that possible.
Also kill a copypasted spurious space in both functions while at it.
...
+/* Multipage variants of the above prefault helpers, useful if more than
+ * PAGE_SIZE of date needs to be prefaulted. These are separate from the
above
+ * functions (which only handle up to PAGE_SIZE) to avoid clobbering the
+ * filemap.c hotpaths. */
Like this please:
/*
* Multipage variants of the above prefault helpers, useful if more than
* PAGE_SIZE of date needs to be prefaulted. These are separate from the above
* functions (which only handle up to PAGE_SIZE) to avoid clobbering the
* filemap.c hotpaths.
*/
and s/date/data/
+static inline int fault_in_multipages_writeable(char __user *uaddr, int size)
+{
+ int ret;
+ const char __user *end = uaddr + size - 1;
+
+ if (unlikely(size == 0))
+ return 0;
+
+ /*
+ * Writing zeroes into userspace here is OK, because we know that if
+ * the zero gets there, we'll be overwriting it.
+ */
Yeah, like that.
+ while (uaddr = end) {
+ ret = __put_user(0, uaddr);
+ if (ret != 0)
+ return ret;
+ uaddr += PAGE_SIZE;
+ }
+
+ /* Check whether the range spilled into the next page. */
+ if (((unsigned long)uaddr PAGE_MASK) ==
+ ((unsigned long)end PAGE_MASK))
+ ret = __put_user(0, end);
+
+ return ret;
+}
+
+static inline int fault_in_multipages_readable(const char __user *uaddr,
+int size)
+{
+ volatile char c;
+ int ret;
+ const char __user *end = uaddr + size - 1;
+
+ if (unlikely(size == 0))
+ return 0;
+
+ while (uaddr = end) {
+ ret = __get_user(c, uaddr);
+ if (ret != 0)
+ return ret;
+ uaddr += PAGE_SIZE;
+ }
+
+ /* Check whether the range spilled into the next page. */
+ if (((unsigned long)uaddr PAGE_MASK) ==
+ ((unsigned long)end PAGE_MASK)) {
+ ret = __get_user(c, end);
+ (void)c;
+ }
+
+ return ret;
+}
Please merge it via the DRI tree.
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[PATCH] mm: extend prefault helpers to fault in more than PAGE_SIZE
On Thu, 1 Mar 2012 00:14:53 +0100 Daniel Vetter wrote: > I'll redo this patch by adding _multipage versions of these 2 functions > for i915. OK, but I hope "for i915" doesn't mean "private to"! Put 'em in pagemap.h, for maintenance reasons and because they are generic. Making them inline is a bit sad, but that's OK for now - they have few callsites.
[PATCH] mm: extend prefault helpers to fault in more than PAGE_SIZE
drm/i915 wants to read/write more than one page in its fastpath
and hence needs to prefault more than PAGE_SIZE bytes.
I've checked the callsites and they all already clamp size when
calling fault_in_pages_* to the same as for the subsequent
__copy_to|from_user and hence don't rely on the implicit clamping
to PAGE_SIZE.
Also kill a copy spurious space in both functions while at it.
v2: As suggested by Andrew Morton, add a multipage parameter to both
functions to avoid the additional branch for the pagemap.c hotpath.
My gcc 4.6 here seems to dtrt and indeed reap these branches where not
needed.
Cc: linux-mm at kvack.org
Signed-off-by: Daniel Vetter
---
drivers/gpu/drm/i915/i915_gem.c|4 +-
drivers/gpu/drm/i915/i915_gem_execbuffer.c |2 +-
fs/pipe.c |4 +-
fs/splice.c|2 +-
include/linux/pagemap.h| 39 ++-
mm/filemap.c |4 +-
6 files changed, 34 insertions(+), 21 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 544e528..9b200f4e 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -436,7 +436,7 @@ i915_gem_shmem_pread(struct drm_device *dev,
mutex_unlock(>struct_mutex);
if (!prefaulted) {
- ret = fault_in_pages_writeable(user_data, remain);
+ ret = fault_in_pages_writeable(user_data, remain, true);
/* Userspace is tricking us, but we've already clobbered
* its pages with the prefault and promised to write the
* data up to the first fault. Hence ignore any errors
@@ -823,7 +823,7 @@ i915_gem_pwrite_ioctl(struct drm_device *dev, void *data,
return -EFAULT;
ret = fault_in_pages_readable((char __user *)(uintptr_t)args->data_ptr,
- args->size);
+ args->size, true);
if (ret)
return -EFAULT;
diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index 81687af..5f0b685 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -955,7 +955,7 @@ validate_exec_list(struct drm_i915_gem_exec_object2 *exec,
if (!access_ok(VERIFY_WRITE, ptr, length))
return -EFAULT;
- if (fault_in_pages_readable(ptr, length))
+ if (fault_in_pages_readable(ptr, length, true))
return -EFAULT;
}
diff --git a/fs/pipe.c b/fs/pipe.c
index a932ced..b29f71c 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -167,7 +167,7 @@ static int iov_fault_in_pages_write(struct iovec *iov,
unsigned long len)
unsigned long this_len;
this_len = min_t(unsigned long, len, iov->iov_len);
- if (fault_in_pages_writeable(iov->iov_base, this_len))
+ if (fault_in_pages_writeable(iov->iov_base, this_len, false))
break;
len -= this_len;
@@ -189,7 +189,7 @@ static void iov_fault_in_pages_read(struct iovec *iov,
unsigned long len)
unsigned long this_len;
this_len = min_t(unsigned long, len, iov->iov_len);
- fault_in_pages_readable(iov->iov_base, this_len);
+ fault_in_pages_readable(iov->iov_base, this_len, false);
len -= this_len;
iov++;
}
diff --git a/fs/splice.c b/fs/splice.c
index 1ec0493..e919d78 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -1491,7 +1491,7 @@ static int pipe_to_user(struct pipe_inode_info *pipe,
struct pipe_buffer *buf,
* See if we can use the atomic maps, by prefaulting in the
* pages and doing an atomic copy
*/
- if (!fault_in_pages_writeable(sd->u.userptr, sd->len)) {
+ if (!fault_in_pages_writeable(sd->u.userptr, sd->len, false)) {
src = buf->ops->map(pipe, buf, 1);
ret = __copy_to_user_inatomic(sd->u.userptr, src + buf->offset,
sd->len);
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index cfaaa69..60ac5c5 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -403,11 +403,14 @@ extern void add_page_wait_queue(struct page *page,
wait_queue_t *waiter);
* Fault a userspace page into pagetables. Return non-zero on a fault.
*
* This assumes that two userspace pages are always sufficient. That's
- * not true if PAGE_CACHE_SIZE > PAGE_SIZE.
+ * not true if PAGE_CACHE_SIZE > PAGE_SIZE. If more than PAGE_SIZE needs to be
+ * prefaulted, set multipage to true.
*/
-static inline int fault_in_pages_writeable(char __user *uaddr, int size)
+static inline int
[PATCH] mm: extend prefault helpers to fault in more than PAGE_SIZE
On Wed, 29 Feb 2012 15:03:31 +0100
Daniel Vetter wrote:
> drm/i915 wants to read/write more than one page in its fastpath
> and hence needs to prefault more than PAGE_SIZE bytes.
>
> I've checked the callsites and they all already clamp size when
> calling fault_in_pages_* to the same as for the subsequent
> __copy_to|from_user and hence don't rely on the implicit clamping
> to PAGE_SIZE.
>
> Also kill a copy spurious space in both functions while at it.
>
> v2: As suggested by Andrew Morton, add a multipage parameter to both
> functions to avoid the additional branch for the pagemap.c hotpath.
> My gcc 4.6 here seems to dtrt and indeed reap these branches where not
> needed.
>
I don't think this produced a very good result :(
>
> ...
>
> -static inline int fault_in_pages_writeable(char __user *uaddr, int size)
> +static inline int fault_in_pages_writeable(char __user *uaddr, int size,
> +bool multipage)
> {
> int ret;
> + char __user *end = uaddr + size - 1;
>
> if (unlikely(size == 0))
> return 0;
> @@ -416,36 +419,46 @@ static inline int fault_in_pages_writeable(char __user
> *uaddr, int size)
>* Writing zeroes into userspace here is OK, because we know that if
>* the zero gets there, we'll be overwriting it.
>*/
> - ret = __put_user(0, uaddr);
> - if (ret == 0) {
> - char __user *end = uaddr + size - 1;
> + do {
> + ret = __put_user(0, uaddr);
> + if (ret != 0)
> + return ret;
> + uaddr += PAGE_SIZE;
> + } while (multipage && uaddr <= end);
>
> + if (ret == 0) {
> /*
>* If the page was already mapped, this will get a cache miss
>* for sure, so try to avoid doing it.
>*/
> - if (((unsigned long)uaddr & PAGE_MASK) !=
> + if (((unsigned long)uaddr & PAGE_MASK) ==
> ((unsigned long)end & PAGE_MASK))
> - ret = __put_user(0, end);
> + ret = __put_user(0, end);
> }
> return ret;
> }
One effect of this change for the filemap.c callsite is that `uaddr'
now gets incremented by PAGE_SIZE. That happens to not break anything
because we then mask `uaddr' with PAGE_MASK, and if gcc were really
smart, it could remove that addition. But it's a bit ugly.
Ideally the patch would have no effect upon filemap.o size, but with an
allmodconfig config I'm seeing
textdata bss dec hex filename
22876 1187344 303387682 mm/filemap.o(before)
22925 1187392 3043576e3 mm/filemap.o(after)
so we are adding read()/write() overhead, and bss mysteriously got larger.
Can we improve on this? Even if it's some dumb
static inline int fault_in_pages_writeable(char __user *uaddr, int size,
bool multipage)
{
if (multipage) {
do-this
} else {
do-that
}
}
the code duplication between do-this and do-that is regrettable, but at
least it's all in the same place in the same file, so we won't
accidentally introduce skew later on.
Alternatively, add a separate fault_in_multi_pages_writeable() to
pagemap.h. I have a bad feeling this is what your original patch did!
(But we *should* be able to make this work! Why did this version of
the patch go so wrong?)
[PATCH] mm: extend prefault helpers to fault in more than PAGE_SIZE
drm/i915 wants to read/write more than one page in its fastpath
and hence needs to prefault more than PAGE_SIZE bytes.
I've checked the callsites and they all already clamp size when
calling fault_in_pages_* to the same as for the subsequent
__copy_to|from_user and hence don't rely on the implicit clamping
to PAGE_SIZE.
Also kill a copypasted spurious space in both functions while at it.
v2: As suggested by Andrew Morton, add a multipage parameter to both
functions to avoid the additional branch for the pagemap.c hotpath.
My gcc 4.6 here seems to dtrt and indeed reap these branches where not
needed.
Cc: linux...@kvack.org
Signed-off-by: Daniel Vetter daniel.vet...@ffwll.ch
---
drivers/gpu/drm/i915/i915_gem.c|4 +-
drivers/gpu/drm/i915/i915_gem_execbuffer.c |2 +-
fs/pipe.c |4 +-
fs/splice.c|2 +-
include/linux/pagemap.h| 39 ++-
mm/filemap.c |4 +-
6 files changed, 34 insertions(+), 21 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 544e528..9b200f4e 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -436,7 +436,7 @@ i915_gem_shmem_pread(struct drm_device *dev,
mutex_unlock(dev-struct_mutex);
if (!prefaulted) {
- ret = fault_in_pages_writeable(user_data, remain);
+ ret = fault_in_pages_writeable(user_data, remain, true);
/* Userspace is tricking us, but we've already clobbered
* its pages with the prefault and promised to write the
* data up to the first fault. Hence ignore any errors
@@ -823,7 +823,7 @@ i915_gem_pwrite_ioctl(struct drm_device *dev, void *data,
return -EFAULT;
ret = fault_in_pages_readable((char __user *)(uintptr_t)args-data_ptr,
- args-size);
+ args-size, true);
if (ret)
return -EFAULT;
diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index 81687af..5f0b685 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -955,7 +955,7 @@ validate_exec_list(struct drm_i915_gem_exec_object2 *exec,
if (!access_ok(VERIFY_WRITE, ptr, length))
return -EFAULT;
- if (fault_in_pages_readable(ptr, length))
+ if (fault_in_pages_readable(ptr, length, true))
return -EFAULT;
}
diff --git a/fs/pipe.c b/fs/pipe.c
index a932ced..b29f71c 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -167,7 +167,7 @@ static int iov_fault_in_pages_write(struct iovec *iov,
unsigned long len)
unsigned long this_len;
this_len = min_t(unsigned long, len, iov-iov_len);
- if (fault_in_pages_writeable(iov-iov_base, this_len))
+ if (fault_in_pages_writeable(iov-iov_base, this_len, false))
break;
len -= this_len;
@@ -189,7 +189,7 @@ static void iov_fault_in_pages_read(struct iovec *iov,
unsigned long len)
unsigned long this_len;
this_len = min_t(unsigned long, len, iov-iov_len);
- fault_in_pages_readable(iov-iov_base, this_len);
+ fault_in_pages_readable(iov-iov_base, this_len, false);
len -= this_len;
iov++;
}
diff --git a/fs/splice.c b/fs/splice.c
index 1ec0493..e919d78 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -1491,7 +1491,7 @@ static int pipe_to_user(struct pipe_inode_info *pipe,
struct pipe_buffer *buf,
* See if we can use the atomic maps, by prefaulting in the
* pages and doing an atomic copy
*/
- if (!fault_in_pages_writeable(sd-u.userptr, sd-len)) {
+ if (!fault_in_pages_writeable(sd-u.userptr, sd-len, false)) {
src = buf-ops-map(pipe, buf, 1);
ret = __copy_to_user_inatomic(sd-u.userptr, src + buf-offset,
sd-len);
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index cfaaa69..60ac5c5 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -403,11 +403,14 @@ extern void add_page_wait_queue(struct page *page,
wait_queue_t *waiter);
* Fault a userspace page into pagetables. Return non-zero on a fault.
*
* This assumes that two userspace pages are always sufficient. That's
- * not true if PAGE_CACHE_SIZE PAGE_SIZE.
+ * not true if PAGE_CACHE_SIZE PAGE_SIZE. If more than PAGE_SIZE needs to be
+ * prefaulted, set multipage to true.
*/
-static inline int fault_in_pages_writeable(char __user *uaddr, int size)
+static inline int
Re: [PATCH] mm: extend prefault helpers to fault in more than PAGE_SIZE
On Wed, 29 Feb 2012 15:03:31 +0100
Daniel Vetter daniel.vet...@ffwll.ch wrote:
drm/i915 wants to read/write more than one page in its fastpath
and hence needs to prefault more than PAGE_SIZE bytes.
I've checked the callsites and they all already clamp size when
calling fault_in_pages_* to the same as for the subsequent
__copy_to|from_user and hence don't rely on the implicit clamping
to PAGE_SIZE.
Also kill a copypasted spurious space in both functions while at it.
v2: As suggested by Andrew Morton, add a multipage parameter to both
functions to avoid the additional branch for the pagemap.c hotpath.
My gcc 4.6 here seems to dtrt and indeed reap these branches where not
needed.
I don't think this produced a very good result :(
...
-static inline int fault_in_pages_writeable(char __user *uaddr, int size)
+static inline int fault_in_pages_writeable(char __user *uaddr, int size,
+bool multipage)
{
int ret;
+ char __user *end = uaddr + size - 1;
if (unlikely(size == 0))
return 0;
@@ -416,36 +419,46 @@ static inline int fault_in_pages_writeable(char __user
*uaddr, int size)
* Writing zeroes into userspace here is OK, because we know that if
* the zero gets there, we'll be overwriting it.
*/
- ret = __put_user(0, uaddr);
- if (ret == 0) {
- char __user *end = uaddr + size - 1;
+ do {
+ ret = __put_user(0, uaddr);
+ if (ret != 0)
+ return ret;
+ uaddr += PAGE_SIZE;
+ } while (multipage uaddr = end);
+ if (ret == 0) {
/*
* If the page was already mapped, this will get a cache miss
* for sure, so try to avoid doing it.
*/
- if (((unsigned long)uaddr PAGE_MASK) !=
+ if (((unsigned long)uaddr PAGE_MASK) ==
((unsigned long)end PAGE_MASK))
- ret = __put_user(0, end);
+ ret = __put_user(0, end);
}
return ret;
}
One effect of this change for the filemap.c callsite is that `uaddr'
now gets incremented by PAGE_SIZE. That happens to not break anything
because we then mask `uaddr' with PAGE_MASK, and if gcc were really
smart, it could remove that addition. But it's a bit ugly.
Ideally the patch would have no effect upon filemap.o size, but with an
allmodconfig config I'm seeing
textdata bss dec hex filename
22876 1187344 303387682 mm/filemap.o(before)
22925 1187392 3043576e3 mm/filemap.o(after)
so we are adding read()/write() overhead, and bss mysteriously got larger.
Can we improve on this? Even if it's some dumb
static inline int fault_in_pages_writeable(char __user *uaddr, int size,
bool multipage)
{
if (multipage) {
do-this
} else {
do-that
}
}
the code duplication between do-this and do-that is regrettable, but at
least it's all in the same place in the same file, so we won't
accidentally introduce skew later on.
Alternatively, add a separate fault_in_multi_pages_writeable() to
pagemap.h. I have a bad feeling this is what your original patch did!
(But we *should* be able to make this work! Why did this version of
the patch go so wrong?)
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Re: [PATCH] mm: extend prefault helpers to fault in more than PAGE_SIZE
On Wed, Feb 29, 2012 at 03:01:46PM -0800, Andrew Morton wrote:
On Wed, 29 Feb 2012 15:03:31 +0100
Daniel Vetter daniel.vet...@ffwll.ch wrote:
drm/i915 wants to read/write more than one page in its fastpath
and hence needs to prefault more than PAGE_SIZE bytes.
I've checked the callsites and they all already clamp size when
calling fault_in_pages_* to the same as for the subsequent
__copy_to|from_user and hence don't rely on the implicit clamping
to PAGE_SIZE.
Also kill a copypasted spurious space in both functions while at it.
v2: As suggested by Andrew Morton, add a multipage parameter to both
functions to avoid the additional branch for the pagemap.c hotpath.
My gcc 4.6 here seems to dtrt and indeed reap these branches where not
needed.
I don't think this produced a very good result :(
And I halfway expected this mail here ;-)
...
-static inline int fault_in_pages_writeable(char __user *uaddr, int size)
+static inline int fault_in_pages_writeable(char __user *uaddr, int size,
+ bool multipage)
{
int ret;
+ char __user *end = uaddr + size - 1;
if (unlikely(size == 0))
return 0;
@@ -416,36 +419,46 @@ static inline int fault_in_pages_writeable(char
__user *uaddr, int size)
* Writing zeroes into userspace here is OK, because we know that if
* the zero gets there, we'll be overwriting it.
*/
- ret = __put_user(0, uaddr);
- if (ret == 0) {
- char __user *end = uaddr + size - 1;
+ do {
+ ret = __put_user(0, uaddr);
+ if (ret != 0)
+ return ret;
+ uaddr += PAGE_SIZE;
+ } while (multipage uaddr = end);
+ if (ret == 0) {
/*
* If the page was already mapped, this will get a cache miss
* for sure, so try to avoid doing it.
*/
- if (((unsigned long)uaddr PAGE_MASK) !=
+ if (((unsigned long)uaddr PAGE_MASK) ==
((unsigned long)end PAGE_MASK))
- ret = __put_user(0, end);
+ ret = __put_user(0, end);
}
return ret;
}
One effect of this change for the filemap.c callsite is that `uaddr'
now gets incremented by PAGE_SIZE. That happens to not break anything
because we then mask `uaddr' with PAGE_MASK, and if gcc were really
smart, it could remove that addition. But it's a bit ugly.
Yep, gcc is not clever enough to reap the addl on uaddr (and change the
check for 'do we need to fault the 2nd page to' from jne to je again).
I've checked that before submitting - maybe should have mentioned this.
Ideally the patch would have no effect upon filemap.o size, but with an
allmodconfig config I'm seeing
textdata bss dec hex filename
22876 1187344 303387682 mm/filemap.o (before)
22925 1187392 3043576e3 mm/filemap.o (after)
so we are adding read()/write() overhead, and bss mysteriously got larger.
Can we improve on this? Even if it's some dumb
static inline int fault_in_pages_writeable(char __user *uaddr, int size,
bool multipage)
{
if (multipage) {
do-this
} else {
do-that
}
}
the code duplication between do-this and do-that is regrettable, but at
least it's all in the same place in the same file, so we won't
accidentally introduce skew later on.
Alternatively, add a separate fault_in_multi_pages_writeable() to
pagemap.h. I have a bad feeling this is what your original patch did!
(But we *should* be able to make this work! Why did this version of
the patch go so wrong?)
Well, I couldn't reconcile the non-multipage with the multipage versions
of these functions - at least not without changing them slightly (like
this patch here does). Which is why I've asked you whether I should just
add a new multipage version of these. I personally deem your proposal of
using and if (multipage) with no shared code too ugly. But you've shot at
it a bit, so I've figured that this version here is what you want.
I'll redo this patch by adding _multipage versions of these 2 functions
for i915.
Yours, Daniel
--
Daniel Vetter
Mail: dan...@ffwll.ch
Mobile: +41 (0)79 365 57 48
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Re: [PATCH] mm: extend prefault helpers to fault in more than PAGE_SIZE
On Thu, 1 Mar 2012 00:14:53 +0100 Daniel Vetter dan...@ffwll.ch wrote: I'll redo this patch by adding _multipage versions of these 2 functions for i915. OK, but I hope for i915 doesn't mean private to! Put 'em in pagemap.h, for maintenance reasons and because they are generic. Making them inline is a bit sad, but that's OK for now - they have few callsites. ___ dri-devel mailing list dri-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/dri-devel
[PATCH] mm: extend prefault helpers to fault in more than PAGE_SIZE
On Thu, Feb 23, 2012 at 02:36:58PM -0800, Andrew Morton wrote:
> On Thu, 16 Feb 2012 13:01:36 +0100
> Daniel Vetter wrote:
>
> > drm/i915 wants to read/write more than one page in its fastpath
> > and hence needs to prefault more than PAGE_SIZE bytes.
> >
> > I've checked the callsites and they all already clamp size when
> > calling fault_in_pages_* to the same as for the subsequent
> > __copy_to|from_user and hence don't rely on the implicit clamping
> > to PAGE_SIZE.
> >
> > Also kill a copy spurious space in both functions while at it.
> >
> > ...
> >
> > --- a/include/linux/pagemap.h
> > +++ b/include/linux/pagemap.h
> > @@ -408,6 +408,7 @@ extern void add_page_wait_queue(struct page *page,
> > wait_queue_t *waiter);
> > static inline int fault_in_pages_writeable(char __user *uaddr, int size)
> > {
> > int ret;
> > + char __user *end = uaddr + size - 1;
> >
> > if (unlikely(size == 0))
> > return 0;
> > @@ -416,17 +417,20 @@ static inline int fault_in_pages_writeable(char
> > __user *uaddr, int size)
> > * Writing zeroes into userspace here is OK, because we know that if
> > * the zero gets there, we'll be overwriting it.
> > */
> > - ret = __put_user(0, uaddr);
> > + while (uaddr <= end) {
> > + ret = __put_user(0, uaddr);
> > + if (ret != 0)
> > + return ret;
> > + uaddr += PAGE_SIZE;
> > + }
>
> The callsites in filemap.c are pretty hot paths, which is why this
> thing remains explicitly inlined. I think it would be worth adding a
> bit of code here to avoid adding a pointless test-n-branch and larger
> cache footprint to read() and write().
>
> A way of doing that is to add another argument to these functions, say
> "bool multipage". Change the code to do
>
> if (multipage) {
> while (uaddr <= end) {
> ...
> }
> }
>
> and change the callsites to pass in constant "true" or "false". Then
> compile it up and manually check that the compiler completely removed
> the offending code from the filemap.c callsites.
>
> Wanna have a think about that? If it all looks OK then please be sure
> to add code comments explaining why we did this.
I wasn't really happy with the added branch either, but failed to come up
with a trick to avoid it. Imho adding new _multipage variants of these
functions instead of adding a constant argument is simpler because the
functions don't really share much thanks to the block below. I'll see what
it looks like (and obviously add a comment explaining what's going on).
> > if (ret == 0) {
> > - char __user *end = uaddr + size - 1;
> > -
> > /*
> > * If the page was already mapped, this will get a cache miss
> > * for sure, so try to avoid doing it.
> > */
> > - if (((unsigned long)uaddr & PAGE_MASK) !=
> > + if (((unsigned long)uaddr & PAGE_MASK) ==
> > ((unsigned long)end & PAGE_MASK))
>
> Maybe I'm having a dim day, but I don't immediately see why != got
> turned into ==.
Because of the loop uaddr will now point one page beyond the last
prefaulted page. To check whether end spilled into a new page we therefore
need to check whether uaddr and end are in the same pfn. Before uaddr
wasn't changed and hence the checking for a different pfn worked
correctly.
> Once we have this settled I'd suggest that the patch be carried in
> whatever-git-tree-needs-it.
Thanks for the comments.
Yours, Daniel
--
Daniel Vetter
Mail: daniel at ffwll.ch
Mobile: +41 (0)79 365 57 48
[PATCH] mm: extend prefault helpers to fault in more than PAGE_SIZE
On Fri, 24 Feb 2012 14:34:31 +0100
Daniel Vetter wrote:
> > > --- a/include/linux/pagemap.h
> > > +++ b/include/linux/pagemap.h
> > > @@ -408,6 +408,7 @@ extern void add_page_wait_queue(struct page *page,
> > > wait_queue_t *waiter);
> > > static inline int fault_in_pages_writeable(char __user *uaddr, int size)
> > > {
> > > int ret;
> > > + char __user *end = uaddr + size - 1;
> > >
> > > if (unlikely(size == 0))
> > > return 0;
> > > @@ -416,17 +417,20 @@ static inline int fault_in_pages_writeable(char
> > > __user *uaddr, int size)
> > >* Writing zeroes into userspace here is OK, because we know that if
> > >* the zero gets there, we'll be overwriting it.
> > >*/
> > > - ret = __put_user(0, uaddr);
> > > + while (uaddr <= end) {
> > > + ret = __put_user(0, uaddr);
> > > + if (ret != 0)
> > > + return ret;
> > > + uaddr += PAGE_SIZE;
> > > + }
> >
> > The callsites in filemap.c are pretty hot paths, which is why this
> > thing remains explicitly inlined. I think it would be worth adding a
> > bit of code here to avoid adding a pointless test-n-branch and larger
> > cache footprint to read() and write().
> >
> > A way of doing that is to add another argument to these functions, say
> > "bool multipage". Change the code to do
> >
> > if (multipage) {
> > while (uaddr <= end) {
> > ...
> > }
> > }
> >
> > and change the callsites to pass in constant "true" or "false". Then
> > compile it up and manually check that the compiler completely removed
> > the offending code from the filemap.c callsites.
> >
> > Wanna have a think about that? If it all looks OK then please be sure
> > to add code comments explaining why we did this.
>
> I wasn't really happy with the added branch either, but failed to come up
> with a trick to avoid it. Imho adding new _multipage variants of these
> functions instead of adding a constant argument is simpler because the
> functions don't really share much thanks to the block below. I'll see what
> it looks like (and obviously add a comment explaining what's going on).
well... that's just syntactic sugar:
static inline int __fault_in_pages_writeable(char __user *uaddr, int size, bool
multipage)
{
...
}
static inline int fault_in_pages_writeable(char __user *uaddr, int size)
{
return __fault_in_pages_writeable(uaddr, size, false);
}
static inline int fault_in_multipages_writeable(char __user *uaddr, int size)
{
return __fault_in_pages_writeable(uaddr, size, true);
}
which I don't think is worth bothering with given the very small number
of callsites.
Re: [PATCH] mm: extend prefault helpers to fault in more than PAGE_SIZE
On Thu, Feb 23, 2012 at 02:36:58PM -0800, Andrew Morton wrote:
On Thu, 16 Feb 2012 13:01:36 +0100
Daniel Vetter daniel.vet...@ffwll.ch wrote:
drm/i915 wants to read/write more than one page in its fastpath
and hence needs to prefault more than PAGE_SIZE bytes.
I've checked the callsites and they all already clamp size when
calling fault_in_pages_* to the same as for the subsequent
__copy_to|from_user and hence don't rely on the implicit clamping
to PAGE_SIZE.
Also kill a copypasted spurious space in both functions while at it.
...
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -408,6 +408,7 @@ extern void add_page_wait_queue(struct page *page,
wait_queue_t *waiter);
static inline int fault_in_pages_writeable(char __user *uaddr, int size)
{
int ret;
+ char __user *end = uaddr + size - 1;
if (unlikely(size == 0))
return 0;
@@ -416,17 +417,20 @@ static inline int fault_in_pages_writeable(char
__user *uaddr, int size)
* Writing zeroes into userspace here is OK, because we know that if
* the zero gets there, we'll be overwriting it.
*/
- ret = __put_user(0, uaddr);
+ while (uaddr = end) {
+ ret = __put_user(0, uaddr);
+ if (ret != 0)
+ return ret;
+ uaddr += PAGE_SIZE;
+ }
The callsites in filemap.c are pretty hot paths, which is why this
thing remains explicitly inlined. I think it would be worth adding a
bit of code here to avoid adding a pointless test-n-branch and larger
cache footprint to read() and write().
A way of doing that is to add another argument to these functions, say
bool multipage. Change the code to do
if (multipage) {
while (uaddr = end) {
...
}
}
and change the callsites to pass in constant true or false. Then
compile it up and manually check that the compiler completely removed
the offending code from the filemap.c callsites.
Wanna have a think about that? If it all looks OK then please be sure
to add code comments explaining why we did this.
I wasn't really happy with the added branch either, but failed to come up
with a trick to avoid it. Imho adding new _multipage variants of these
functions instead of adding a constant argument is simpler because the
functions don't really share much thanks to the block below. I'll see what
it looks like (and obviously add a comment explaining what's going on).
if (ret == 0) {
- char __user *end = uaddr + size - 1;
-
/*
* If the page was already mapped, this will get a cache miss
* for sure, so try to avoid doing it.
*/
- if (((unsigned long)uaddr PAGE_MASK) !=
+ if (((unsigned long)uaddr PAGE_MASK) ==
((unsigned long)end PAGE_MASK))
Maybe I'm having a dim day, but I don't immediately see why != got
turned into ==.
Because of the loop uaddr will now point one page beyond the last
prefaulted page. To check whether end spilled into a new page we therefore
need to check whether uaddr and end are in the same pfn. Before uaddr
wasn't changed and hence the checking for a different pfn worked
correctly.
Once we have this settled I'd suggest that the patch be carried in
whatever-git-tree-needs-it.
Thanks for the comments.
Yours, Daniel
--
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Mail: dan...@ffwll.ch
Mobile: +41 (0)79 365 57 48
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Re: [PATCH] mm: extend prefault helpers to fault in more than PAGE_SIZE
On Fri, 24 Feb 2012 14:34:31 +0100
Daniel Vetter dan...@ffwll.ch wrote:
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -408,6 +408,7 @@ extern void add_page_wait_queue(struct page *page,
wait_queue_t *waiter);
static inline int fault_in_pages_writeable(char __user *uaddr, int size)
{
int ret;
+ char __user *end = uaddr + size - 1;
if (unlikely(size == 0))
return 0;
@@ -416,17 +417,20 @@ static inline int fault_in_pages_writeable(char
__user *uaddr, int size)
* Writing zeroes into userspace here is OK, because we know that if
* the zero gets there, we'll be overwriting it.
*/
- ret = __put_user(0, uaddr);
+ while (uaddr = end) {
+ ret = __put_user(0, uaddr);
+ if (ret != 0)
+ return ret;
+ uaddr += PAGE_SIZE;
+ }
The callsites in filemap.c are pretty hot paths, which is why this
thing remains explicitly inlined. I think it would be worth adding a
bit of code here to avoid adding a pointless test-n-branch and larger
cache footprint to read() and write().
A way of doing that is to add another argument to these functions, say
bool multipage. Change the code to do
if (multipage) {
while (uaddr = end) {
...
}
}
and change the callsites to pass in constant true or false. Then
compile it up and manually check that the compiler completely removed
the offending code from the filemap.c callsites.
Wanna have a think about that? If it all looks OK then please be sure
to add code comments explaining why we did this.
I wasn't really happy with the added branch either, but failed to come up
with a trick to avoid it. Imho adding new _multipage variants of these
functions instead of adding a constant argument is simpler because the
functions don't really share much thanks to the block below. I'll see what
it looks like (and obviously add a comment explaining what's going on).
well... that's just syntactic sugar:
static inline int __fault_in_pages_writeable(char __user *uaddr, int size, bool
multipage)
{
...
}
static inline int fault_in_pages_writeable(char __user *uaddr, int size)
{
return __fault_in_pages_writeable(uaddr, size, false);
}
static inline int fault_in_multipages_writeable(char __user *uaddr, int size)
{
return __fault_in_pages_writeable(uaddr, size, true);
}
which I don't think is worth bothering with given the very small number
of callsites.
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[PATCH] mm: extend prefault helpers to fault in more than PAGE_SIZE
On Thu, 16 Feb 2012 13:01:36 +0100
Daniel Vetter wrote:
> drm/i915 wants to read/write more than one page in its fastpath
> and hence needs to prefault more than PAGE_SIZE bytes.
>
> I've checked the callsites and they all already clamp size when
> calling fault_in_pages_* to the same as for the subsequent
> __copy_to|from_user and hence don't rely on the implicit clamping
> to PAGE_SIZE.
>
> Also kill a copy spurious space in both functions while at it.
>
> ...
>
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -408,6 +408,7 @@ extern void add_page_wait_queue(struct page *page,
> wait_queue_t *waiter);
> static inline int fault_in_pages_writeable(char __user *uaddr, int size)
> {
> int ret;
> + char __user *end = uaddr + size - 1;
>
> if (unlikely(size == 0))
> return 0;
> @@ -416,17 +417,20 @@ static inline int fault_in_pages_writeable(char __user
> *uaddr, int size)
>* Writing zeroes into userspace here is OK, because we know that if
>* the zero gets there, we'll be overwriting it.
>*/
> - ret = __put_user(0, uaddr);
> + while (uaddr <= end) {
> + ret = __put_user(0, uaddr);
> + if (ret != 0)
> + return ret;
> + uaddr += PAGE_SIZE;
> + }
The callsites in filemap.c are pretty hot paths, which is why this
thing remains explicitly inlined. I think it would be worth adding a
bit of code here to avoid adding a pointless test-n-branch and larger
cache footprint to read() and write().
A way of doing that is to add another argument to these functions, say
"bool multipage". Change the code to do
if (multipage) {
while (uaddr <= end) {
...
}
}
and change the callsites to pass in constant "true" or "false". Then
compile it up and manually check that the compiler completely removed
the offending code from the filemap.c callsites.
Wanna have a think about that? If it all looks OK then please be sure
to add code comments explaining why we did this.
> if (ret == 0) {
> - char __user *end = uaddr + size - 1;
> -
> /*
>* If the page was already mapped, this will get a cache miss
>* for sure, so try to avoid doing it.
>*/
> - if (((unsigned long)uaddr & PAGE_MASK) !=
> + if (((unsigned long)uaddr & PAGE_MASK) ==
> ((unsigned long)end & PAGE_MASK))
Maybe I'm having a dim day, but I don't immediately see why != got
turned into ==.
Once we have this settled I'd suggest that the patch be carried in
whatever-git-tree-needs-it.
Re: [PATCH] mm: extend prefault helpers to fault in more than PAGE_SIZE
On Thu, 16 Feb 2012 13:01:36 +0100
Daniel Vetter daniel.vet...@ffwll.ch wrote:
drm/i915 wants to read/write more than one page in its fastpath
and hence needs to prefault more than PAGE_SIZE bytes.
I've checked the callsites and they all already clamp size when
calling fault_in_pages_* to the same as for the subsequent
__copy_to|from_user and hence don't rely on the implicit clamping
to PAGE_SIZE.
Also kill a copypasted spurious space in both functions while at it.
...
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -408,6 +408,7 @@ extern void add_page_wait_queue(struct page *page,
wait_queue_t *waiter);
static inline int fault_in_pages_writeable(char __user *uaddr, int size)
{
int ret;
+ char __user *end = uaddr + size - 1;
if (unlikely(size == 0))
return 0;
@@ -416,17 +417,20 @@ static inline int fault_in_pages_writeable(char __user
*uaddr, int size)
* Writing zeroes into userspace here is OK, because we know that if
* the zero gets there, we'll be overwriting it.
*/
- ret = __put_user(0, uaddr);
+ while (uaddr = end) {
+ ret = __put_user(0, uaddr);
+ if (ret != 0)
+ return ret;
+ uaddr += PAGE_SIZE;
+ }
The callsites in filemap.c are pretty hot paths, which is why this
thing remains explicitly inlined. I think it would be worth adding a
bit of code here to avoid adding a pointless test-n-branch and larger
cache footprint to read() and write().
A way of doing that is to add another argument to these functions, say
bool multipage. Change the code to do
if (multipage) {
while (uaddr = end) {
...
}
}
and change the callsites to pass in constant true or false. Then
compile it up and manually check that the compiler completely removed
the offending code from the filemap.c callsites.
Wanna have a think about that? If it all looks OK then please be sure
to add code comments explaining why we did this.
if (ret == 0) {
- char __user *end = uaddr + size - 1;
-
/*
* If the page was already mapped, this will get a cache miss
* for sure, so try to avoid doing it.
*/
- if (((unsigned long)uaddr PAGE_MASK) !=
+ if (((unsigned long)uaddr PAGE_MASK) ==
((unsigned long)end PAGE_MASK))
Maybe I'm having a dim day, but I don't immediately see why != got
turned into ==.
Once we have this settled I'd suggest that the patch be carried in
whatever-git-tree-needs-it.
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[PATCH] mm: extend prefault helpers to fault in more than PAGE_SIZE
On Thu, Feb 16, 2012 at 8:01 PM, Daniel Vetter
wrote:
> @@ -416,17 +417,20 @@ static inline int fault_in_pages_writeable(char __user
> *uaddr, int size)
> ? ? ? ? * Writing zeroes into userspace here is OK, because we know that if
> ? ? ? ? * the zero gets there, we'll be overwriting it.
> ? ? ? ? */
> - ? ? ? ret = __put_user(0, uaddr);
> + ? ? ? while (uaddr <= end) {
> + ? ? ? ? ? ? ? ret = __put_user(0, uaddr);
> + ? ? ? ? ? ? ? if (ret != 0)
> + ? ? ? ? ? ? ? ? ? ? ? return ret;
> + ? ? ? ? ? ? ? uaddr += PAGE_SIZE;
> + ? ? ? }
What if
uaddr & ~PAGE_MASK == PAGE_SIZE -3 &&
end & ~PAGE_MASK == 2
[PATCH] mm: extend prefault helpers to fault in more than PAGE_SIZE
On Thu, Feb 16, 2012 at 09:32:08PM +0800, Hillf Danton wrote:
> On Thu, Feb 16, 2012 at 8:01 PM, Daniel Vetter
> wrote:
> > @@ -416,17 +417,20 @@ static inline int fault_in_pages_writeable(char
> > __user *uaddr, int size)
> > ? ? ? ? * Writing zeroes into userspace here is OK, because we know that if
> > ? ? ? ? * the zero gets there, we'll be overwriting it.
> > ? ? ? ? */
> > - ? ? ? ret = __put_user(0, uaddr);
> > + ? ? ? while (uaddr <= end) {
> > + ? ? ? ? ? ? ? ret = __put_user(0, uaddr);
> > + ? ? ? ? ? ? ? if (ret != 0)
> > + ? ? ? ? ? ? ? ? ? ? ? return ret;
> > + ? ? ? ? ? ? ? uaddr += PAGE_SIZE;
> > + ? ? ? }
>
> What if
> uaddr & ~PAGE_MASK == PAGE_SIZE -3 &&
> end & ~PAGE_MASK == 2
I don't quite follow - can you elaborate upon which issue you're seeing?
-Daniel
--
Daniel Vetter
Mail: daniel at ffwll.ch
Mobile: +41 (0)79 365 57 48
[PATCH] mm: extend prefault helpers to fault in more than PAGE_SIZE
drm/i915 wants to read/write more than one page in its fastpath
and hence needs to prefault more than PAGE_SIZE bytes.
I've checked the callsites and they all already clamp size when
calling fault_in_pages_* to the same as for the subsequent
__copy_to|from_user and hence don't rely on the implicit clamping
to PAGE_SIZE.
Also kill a copy spurious space in both functions while at it.
Cc: linux-mm at kvack.org
Signed-off-by: Daniel Vetter
---
include/linux/pagemap.h | 28 ++--
1 files changed, 18 insertions(+), 10 deletions(-)
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index cfaaa69..689527d 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -408,6 +408,7 @@ extern void add_page_wait_queue(struct page *page,
wait_queue_t *waiter);
static inline int fault_in_pages_writeable(char __user *uaddr, int size)
{
int ret;
+ char __user *end = uaddr + size - 1;
if (unlikely(size == 0))
return 0;
@@ -416,17 +417,20 @@ static inline int fault_in_pages_writeable(char __user
*uaddr, int size)
* Writing zeroes into userspace here is OK, because we know that if
* the zero gets there, we'll be overwriting it.
*/
- ret = __put_user(0, uaddr);
+ while (uaddr <= end) {
+ ret = __put_user(0, uaddr);
+ if (ret != 0)
+ return ret;
+ uaddr += PAGE_SIZE;
+ }
if (ret == 0) {
- char __user *end = uaddr + size - 1;
-
/*
* If the page was already mapped, this will get a cache miss
* for sure, so try to avoid doing it.
*/
- if (((unsigned long)uaddr & PAGE_MASK) !=
+ if (((unsigned long)uaddr & PAGE_MASK) ==
((unsigned long)end & PAGE_MASK))
- ret = __put_user(0, end);
+ ret = __put_user(0, end);
}
return ret;
}
@@ -435,17 +439,21 @@ static inline int fault_in_pages_readable(const char
__user *uaddr, int size)
{
volatile char c;
int ret;
+ const char __user *end = uaddr + size - 1;
if (unlikely(size == 0))
return 0;
- ret = __get_user(c, uaddr);
+ while (uaddr <= end) {
+ ret = __get_user(c, uaddr);
+ if (ret != 0)
+ return ret;
+ uaddr += PAGE_SIZE;
+ }
if (ret == 0) {
- const char __user *end = uaddr + size - 1;
-
- if (((unsigned long)uaddr & PAGE_MASK) !=
+ if (((unsigned long)uaddr & PAGE_MASK) ==
((unsigned long)end & PAGE_MASK)) {
- ret = __get_user(c, end);
+ ret = __get_user(c, end);
(void)c;
}
}
--
1.7.7.5
[PATCH] mm: extend prefault helpers to fault in more than PAGE_SIZE
drm/i915 wants to read/write more than one page in its fastpath
and hence needs to prefault more than PAGE_SIZE bytes.
I've checked the callsites and they all already clamp size when
calling fault_in_pages_* to the same as for the subsequent
__copy_to|from_user and hence don't rely on the implicit clamping
to PAGE_SIZE.
Also kill a copypasted spurious space in both functions while at it.
Cc: linux...@kvack.org
Signed-off-by: Daniel Vetter daniel.vet...@ffwll.ch
---
include/linux/pagemap.h | 28 ++--
1 files changed, 18 insertions(+), 10 deletions(-)
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index cfaaa69..689527d 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -408,6 +408,7 @@ extern void add_page_wait_queue(struct page *page,
wait_queue_t *waiter);
static inline int fault_in_pages_writeable(char __user *uaddr, int size)
{
int ret;
+ char __user *end = uaddr + size - 1;
if (unlikely(size == 0))
return 0;
@@ -416,17 +417,20 @@ static inline int fault_in_pages_writeable(char __user
*uaddr, int size)
* Writing zeroes into userspace here is OK, because we know that if
* the zero gets there, we'll be overwriting it.
*/
- ret = __put_user(0, uaddr);
+ while (uaddr = end) {
+ ret = __put_user(0, uaddr);
+ if (ret != 0)
+ return ret;
+ uaddr += PAGE_SIZE;
+ }
if (ret == 0) {
- char __user *end = uaddr + size - 1;
-
/*
* If the page was already mapped, this will get a cache miss
* for sure, so try to avoid doing it.
*/
- if (((unsigned long)uaddr PAGE_MASK) !=
+ if (((unsigned long)uaddr PAGE_MASK) ==
((unsigned long)end PAGE_MASK))
- ret = __put_user(0, end);
+ ret = __put_user(0, end);
}
return ret;
}
@@ -435,17 +439,21 @@ static inline int fault_in_pages_readable(const char
__user *uaddr, int size)
{
volatile char c;
int ret;
+ const char __user *end = uaddr + size - 1;
if (unlikely(size == 0))
return 0;
- ret = __get_user(c, uaddr);
+ while (uaddr = end) {
+ ret = __get_user(c, uaddr);
+ if (ret != 0)
+ return ret;
+ uaddr += PAGE_SIZE;
+ }
if (ret == 0) {
- const char __user *end = uaddr + size - 1;
-
- if (((unsigned long)uaddr PAGE_MASK) !=
+ if (((unsigned long)uaddr PAGE_MASK) ==
((unsigned long)end PAGE_MASK)) {
- ret = __get_user(c, end);
+ ret = __get_user(c, end);
(void)c;
}
}
--
1.7.7.5
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Re: [PATCH] mm: extend prefault helpers to fault in more than PAGE_SIZE
On Thu, Feb 16, 2012 at 09:32:08PM +0800, Hillf Danton wrote:
On Thu, Feb 16, 2012 at 8:01 PM, Daniel Vetter daniel.vet...@ffwll.ch wrote:
@@ -416,17 +417,20 @@ static inline int fault_in_pages_writeable(char
__user *uaddr, int size)
* Writing zeroes into userspace here is OK, because we know that if
* the zero gets there, we'll be overwriting it.
*/
- ret = __put_user(0, uaddr);
+ while (uaddr = end) {
+ ret = __put_user(0, uaddr);
+ if (ret != 0)
+ return ret;
+ uaddr += PAGE_SIZE;
+ }
What if
uaddr ~PAGE_MASK == PAGE_SIZE -3
end ~PAGE_MASK == 2
I don't quite follow - can you elaborate upon which issue you're seeing?
-Daniel
--
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Mail: dan...@ffwll.ch
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Re: [PATCH] mm: extend prefault helpers to fault in more than PAGE_SIZE
On Thu, Feb 16, 2012 at 8:01 PM, Daniel Vetter daniel.vet...@ffwll.ch wrote:
@@ -416,17 +417,20 @@ static inline int fault_in_pages_writeable(char __user
*uaddr, int size)
* Writing zeroes into userspace here is OK, because we know that if
* the zero gets there, we'll be overwriting it.
*/
- ret = __put_user(0, uaddr);
+ while (uaddr = end) {
+ ret = __put_user(0, uaddr);
+ if (ret != 0)
+ return ret;
+ uaddr += PAGE_SIZE;
+ }
What if
uaddr ~PAGE_MASK == PAGE_SIZE -3
end ~PAGE_MASK == 2
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