Re: [PATCHv2 2/3] i915: convert to new mount API
On 08/08/2019 17:23, Chris Wilson wrote:
Quoting Hugh Dickins (2019-08-08 16:54:16)
On Thu, 8 Aug 2019, Al Viro wrote:
On Wed, Aug 07, 2019 at 08:30:02AM +0200, Christoph Hellwig wrote:
On Tue, Aug 06, 2019 at 12:50:10AM -0700, Hugh Dickins wrote:
Though personally I'm averse to managing "f"objects through
"m"interfaces, which can get ridiculous (notably, MADV_HUGEPAGE works
on the virtual address of a mapping, but the huge-or-not alignment of
that mapping must have been decided previously). In Google we do use
fcntls F_HUGEPAGE and F_NOHUGEPAGE to override on a per-file basis -
one day I'll get to upstreaming those.
Such an interface seems very useful, although the two fcntls seem a bit
odd.
But I think the point here is that the i915 has its own somewhat odd
instance of tmpfs. If we could pass the equivalent of the huge=*
options to shmem_file_setup all that garbage (including the
shmem_file_setup_with_mnt function) could go away.
... or follow shmem_file_super() with whatever that fcntl maps to
internally. I would really love to get rid of that i915 kludge.
As to the immediate problem of i915_gemfs using remount_fs on linux-next,
IIUC, all that is necessary at the moment is the deletions patch below
(but I'd prefer that to come from the i915 folks). Since gemfs has no
need to change the huge option from its default to its default.
As to the future of when they get back to wanting huge pages in gemfs,
yes, that can probably best be arranged by using the internals of an
fcntl F_HUGEPAGE on those objects that would benefit from it.
Though my intention there was that the "huge=never" default ought
to continue to refuse to give huge pages, even when asked by fcntl.
So a little hackery may still be required, to allow the i915_gemfs
internal mount to get huge pages when a user mount would not.
As to whether shmem_file_setup_with_mnt() needs to live: I've given
that no thought, but accept that shm_mnt is such a ragbag of different
usages, that i915 is right to prefer their own separate gemfs mount.
Hugh
--- mmotm/drivers/gpu/drm/i915/gem/i915_gemfs.c 2019-07-21 19:40:16.573703780
-0700
+++ linux/drivers/gpu/drm/i915/gem/i915_gemfs.c 2019-08-08 07:19:23.967689058
-0700
@@ -24,28 +24,6 @@ int i915_gemfs_init(struct drm_i915_priv
if (IS_ERR(gemfs))
return PTR_ERR(gemfs);
- /*
-* Enable huge-pages for objects that are at least HPAGE_PMD_SIZE, most
-* likely 2M. Note that within_size may overallocate huge-pages, if say
-* we allocate an object of size 2M + 4K, we may get 2M + 2M, but under
-* memory pressure shmem should split any huge-pages which can be
-* shrunk.
-*/
-
- if (has_transparent_hugepage()) {
- struct super_block *sb = gemfs->mnt_sb;
- /* FIXME: Disabled until we get W/A for read BW issue. */
- char options[] = "huge=never";
- int flags = 0;
- int err;
-
- err = sb->s_op->remount_fs(sb, , options);
- if (err) {
- kern_unmount(gemfs);
- return err;
- }
- }
That's perfectly fine; we should probably leave a hint as to why gemfs
exists and include the suggestion of looking at per-file hugepage
controls.
Matthew, how does this affect your current plans? If at all?
Fine with me.
-Chris
Re: [PATCHv2 2/3] i915: convert to new mount API
Quoting Hugh Dickins (2019-08-08 16:54:16)
> On Thu, 8 Aug 2019, Al Viro wrote:
> > On Wed, Aug 07, 2019 at 08:30:02AM +0200, Christoph Hellwig wrote:
> > > On Tue, Aug 06, 2019 at 12:50:10AM -0700, Hugh Dickins wrote:
> > > > Though personally I'm averse to managing "f"objects through
> > > > "m"interfaces, which can get ridiculous (notably, MADV_HUGEPAGE works
> > > > on the virtual address of a mapping, but the huge-or-not alignment of
> > > > that mapping must have been decided previously). In Google we do use
> > > > fcntls F_HUGEPAGE and F_NOHUGEPAGE to override on a per-file basis -
> > > > one day I'll get to upstreaming those.
> > >
> > > Such an interface seems very useful, although the two fcntls seem a bit
> > > odd.
> > >
> > > But I think the point here is that the i915 has its own somewhat odd
> > > instance of tmpfs. If we could pass the equivalent of the huge=*
> > > options to shmem_file_setup all that garbage (including the
> > > shmem_file_setup_with_mnt function) could go away.
> >
> > ... or follow shmem_file_super() with whatever that fcntl maps to
> > internally. I would really love to get rid of that i915 kludge.
>
> As to the immediate problem of i915_gemfs using remount_fs on linux-next,
> IIUC, all that is necessary at the moment is the deletions patch below
> (but I'd prefer that to come from the i915 folks). Since gemfs has no
> need to change the huge option from its default to its default.
>
> As to the future of when they get back to wanting huge pages in gemfs,
> yes, that can probably best be arranged by using the internals of an
> fcntl F_HUGEPAGE on those objects that would benefit from it.
>
> Though my intention there was that the "huge=never" default ought
> to continue to refuse to give huge pages, even when asked by fcntl.
> So a little hackery may still be required, to allow the i915_gemfs
> internal mount to get huge pages when a user mount would not.
>
> As to whether shmem_file_setup_with_mnt() needs to live: I've given
> that no thought, but accept that shm_mnt is such a ragbag of different
> usages, that i915 is right to prefer their own separate gemfs mount.
>
> Hugh
>
> --- mmotm/drivers/gpu/drm/i915/gem/i915_gemfs.c 2019-07-21 19:40:16.573703780
> -0700
> +++ linux/drivers/gpu/drm/i915/gem/i915_gemfs.c 2019-08-08 07:19:23.967689058
> -0700
> @@ -24,28 +24,6 @@ int i915_gemfs_init(struct drm_i915_priv
> if (IS_ERR(gemfs))
> return PTR_ERR(gemfs);
>
> - /*
> -* Enable huge-pages for objects that are at least HPAGE_PMD_SIZE,
> most
> -* likely 2M. Note that within_size may overallocate huge-pages, if
> say
> -* we allocate an object of size 2M + 4K, we may get 2M + 2M, but
> under
> -* memory pressure shmem should split any huge-pages which can be
> -* shrunk.
> -*/
> -
> - if (has_transparent_hugepage()) {
> - struct super_block *sb = gemfs->mnt_sb;
> - /* FIXME: Disabled until we get W/A for read BW issue. */
> - char options[] = "huge=never";
> - int flags = 0;
> - int err;
> -
> - err = sb->s_op->remount_fs(sb, , options);
> - if (err) {
> - kern_unmount(gemfs);
> - return err;
> - }
> - }
That's perfectly fine; we should probably leave a hint as to why gemfs
exists and include the suggestion of looking at per-file hugepage
controls.
Matthew, how does this affect your current plans? If at all?
-Chris
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Re: [PATCHv2 2/3] i915: convert to new mount API
On Thu, 8 Aug 2019, Al Viro wrote:
> On Wed, Aug 07, 2019 at 08:30:02AM +0200, Christoph Hellwig wrote:
> > On Tue, Aug 06, 2019 at 12:50:10AM -0700, Hugh Dickins wrote:
> > > Though personally I'm averse to managing "f"objects through
> > > "m"interfaces, which can get ridiculous (notably, MADV_HUGEPAGE works
> > > on the virtual address of a mapping, but the huge-or-not alignment of
> > > that mapping must have been decided previously). In Google we do use
> > > fcntls F_HUGEPAGE and F_NOHUGEPAGE to override on a per-file basis -
> > > one day I'll get to upstreaming those.
> >
> > Such an interface seems very useful, although the two fcntls seem a bit
> > odd.
> >
> > But I think the point here is that the i915 has its own somewhat odd
> > instance of tmpfs. If we could pass the equivalent of the huge=*
> > options to shmem_file_setup all that garbage (including the
> > shmem_file_setup_with_mnt function) could go away.
>
> ... or follow shmem_file_super() with whatever that fcntl maps to
> internally. I would really love to get rid of that i915 kludge.
As to the immediate problem of i915_gemfs using remount_fs on linux-next,
IIUC, all that is necessary at the moment is the deletions patch below
(but I'd prefer that to come from the i915 folks). Since gemfs has no
need to change the huge option from its default to its default.
As to the future of when they get back to wanting huge pages in gemfs,
yes, that can probably best be arranged by using the internals of an
fcntl F_HUGEPAGE on those objects that would benefit from it.
Though my intention there was that the "huge=never" default ought
to continue to refuse to give huge pages, even when asked by fcntl.
So a little hackery may still be required, to allow the i915_gemfs
internal mount to get huge pages when a user mount would not.
As to whether shmem_file_setup_with_mnt() needs to live: I've given
that no thought, but accept that shm_mnt is such a ragbag of different
usages, that i915 is right to prefer their own separate gemfs mount.
Hugh
--- mmotm/drivers/gpu/drm/i915/gem/i915_gemfs.c 2019-07-21 19:40:16.573703780
-0700
+++ linux/drivers/gpu/drm/i915/gem/i915_gemfs.c 2019-08-08 07:19:23.967689058
-0700
@@ -24,28 +24,6 @@ int i915_gemfs_init(struct drm_i915_priv
if (IS_ERR(gemfs))
return PTR_ERR(gemfs);
- /*
-* Enable huge-pages for objects that are at least HPAGE_PMD_SIZE, most
-* likely 2M. Note that within_size may overallocate huge-pages, if say
-* we allocate an object of size 2M + 4K, we may get 2M + 2M, but under
-* memory pressure shmem should split any huge-pages which can be
-* shrunk.
-*/
-
- if (has_transparent_hugepage()) {
- struct super_block *sb = gemfs->mnt_sb;
- /* FIXME: Disabled until we get W/A for read BW issue. */
- char options[] = "huge=never";
- int flags = 0;
- int err;
-
- err = sb->s_op->remount_fs(sb, , options);
- if (err) {
- kern_unmount(gemfs);
- return err;
- }
- }
-
i915->mm.gemfs = gemfs;
return 0;
Re: [PATCHv2 2/3] i915: convert to new mount API
On Wed, Aug 07, 2019 at 08:30:02AM +0200, Christoph Hellwig wrote: > On Tue, Aug 06, 2019 at 12:50:10AM -0700, Hugh Dickins wrote: > > Though personally I'm averse to managing "f"objects through > > "m"interfaces, which can get ridiculous (notably, MADV_HUGEPAGE works > > on the virtual address of a mapping, but the huge-or-not alignment of > > that mapping must have been decided previously). In Google we do use > > fcntls F_HUGEPAGE and F_NOHUGEPAGE to override on a per-file basis - > > one day I'll get to upstreaming those. > > Such an interface seems very useful, although the two fcntls seem a bit > odd. > > But I think the point here is that the i915 has its own somewhat odd > instance of tmpfs. If we could pass the equivalent of the huge=* > options to shmem_file_setup all that garbage (including the > shmem_file_setup_with_mnt function) could go away. ... or follow shmem_file_super() with whatever that fcntl maps to internally. I would really love to get rid of that i915 kludge.
Re: [PATCHv2 2/3] i915: convert to new mount API
On Tue, Aug 06, 2019 at 12:50:10AM -0700, Hugh Dickins wrote: > that mapping must have been decided previously). In Google we do use > fcntls F_HUGEPAGE and F_NOHUGEPAGE to override on a per-file basis - > one day I'll get to upstreaming those. That'd be nice - we could kill the i915 wierd private shmem instance, along with some kludges in mm/shmem.c.
Re: [PATCHv2 2/3] i915: convert to new mount API
On Tue, Aug 06, 2019 at 12:50:10AM -0700, Hugh Dickins wrote: > Though personally I'm averse to managing "f"objects through > "m"interfaces, which can get ridiculous (notably, MADV_HUGEPAGE works > on the virtual address of a mapping, but the huge-or-not alignment of > that mapping must have been decided previously). In Google we do use > fcntls F_HUGEPAGE and F_NOHUGEPAGE to override on a per-file basis - > one day I'll get to upstreaming those. Such an interface seems very useful, although the two fcntls seem a bit odd. But I think the point here is that the i915 has its own somewhat odd instance of tmpfs. If we could pass the equivalent of the huge=* options to shmem_file_setup all that garbage (including the shmem_file_setup_with_mnt function) could go away.
Re: [PATCHv2 2/3] i915: convert to new mount API
On Mon, 5 Aug 2019, Al Viro wrote:
> On Mon, Aug 05, 2019 at 07:12:55PM +0100, Al Viro wrote:
> > On Tue, Aug 06, 2019 at 01:03:06AM +0900, Sergey Senozhatsky wrote:
> > > tmpfs does not set ->remount_fs() anymore and its users need
> > > to be converted to new mount API.
> >
> > Could you explain why the devil do you bother with remount at all?
> > Why not pass the right options when mounting the damn thing?
>
> ... and while we are at it, I really wonder what's going on with
> that gemfs thing - among the other things, this is the only
> user of shmem_file_setup_with_mnt(). Sure, you want your own
> options, but that brings another question - is there any reason
> for having the huge=... per-superblock rather than per-file?
Yes: we want a default for how files of that superblock are to
allocate their pages, without people having to fcntl or advise
each of their files.
Setting aside the weirder options (within_size, advise) and emergency/
testing override (shmem_huge), we want files on an ordinary default
tmpfs (huge=never) to be allocated with small pages (so users with
access to that filesystem will not consume, and will not waste time
and space on consuming, the more valuable huge pages); but files on a
huge=always tmpfs to be allocated with huge pages whenever possible.
Or am I missing your point? Yes, hugeness can certainly be decided
differently per-file, or even per-extent of file. That is already
made possible through "judicious" use of madvise MADV_HUGEPAGE and
MADV_NOHUGEPAGE on mmaps of the file, carried over from anon THP.
Though personally I'm averse to managing "f"objects through
"m"interfaces, which can get ridiculous (notably, MADV_HUGEPAGE works
on the virtual address of a mapping, but the huge-or-not alignment of
that mapping must have been decided previously). In Google we do use
fcntls F_HUGEPAGE and F_NOHUGEPAGE to override on a per-file basis -
one day I'll get to upstreaming those.
Hugh
>
> After all, the readers of ->huge in mm/shmem.c are
> mm/shmem.c:582: (shmem_huge == SHMEM_HUGE_FORCE || sbinfo->huge) &&
> is_huge_enabled(), sbinfo is an explicit argument
>
> mm/shmem.c:1799:switch (sbinfo->huge) {
> shmem_getpage_gfp(), sbinfo comes from inode
>
> mm/shmem.c:2113:if (SHMEM_SB(sb)->huge == SHMEM_HUGE_NEVER)
> shmem_get_unmapped_area(), sb comes from file
>
> mm/shmem.c:3531:if (sbinfo->huge)
> mm/shmem.c:3532:seq_printf(seq, ",huge=%s",
> shmem_format_huge(sbinfo->huge));
> ->show_options()
> mm/shmem.c:3880:switch (sbinfo->huge) {
> shmem_huge_enabled(), sbinfo comes from an inode
>
> And the only caller of is_huge_enabled() is shmem_getattr(), with sbinfo
> picked from inode.
>
> So is there any reason why the hugepage policy can't be per-file, with
> the current being overridable default?
Re: [PATCHv2 2/3] i915: convert to new mount API
On (08/05/19 19:12), Al Viro wrote: [..] > On Tue, Aug 06, 2019 at 01:03:06AM +0900, Sergey Senozhatsky wrote: > > tmpfs does not set ->remount_fs() anymore and its users need > > to be converted to new mount API. > > Could you explain why the devil do you bother with remount at all? I would redirect this question to i915 developers. As far as I know i915 performance suffers with huge pages enabled. > Why not pass the right options when mounting the damn thing? vfs_kern_mount()? It still requires struct file_system_type, which we need to get and put. -ss
Re: [PATCHv2 2/3] i915: convert to new mount API
On Mon, Aug 05, 2019 at 07:12:55PM +0100, Al Viro wrote: > On Tue, Aug 06, 2019 at 01:03:06AM +0900, Sergey Senozhatsky wrote: > > tmpfs does not set ->remount_fs() anymore and its users need > > to be converted to new mount API. > > Could you explain why the devil do you bother with remount at all? > Why not pass the right options when mounting the damn thing? Incidentally, the only remaining modular user of get_fs_type() is the same i915_gemfs.c. And I wonder if we should aim for unexporting the damn thing instead of exporting put_filesystem()... Note that users in tomoyo and apparmor are bogus - they are in the instances of ill-defined method that needs to be split and moved, with the lookups (fs type included) replaced with callers passing the values they look up and will end up using. IOW, outside of core VFS we have very few legitimate users, and the one in kernel/trace might be better off as vfs_submount_by_name().
Re: [PATCHv2 2/3] i915: convert to new mount API
On Mon, Aug 05, 2019 at 07:12:55PM +0100, Al Viro wrote:
> On Tue, Aug 06, 2019 at 01:03:06AM +0900, Sergey Senozhatsky wrote:
> > tmpfs does not set ->remount_fs() anymore and its users need
> > to be converted to new mount API.
>
> Could you explain why the devil do you bother with remount at all?
> Why not pass the right options when mounting the damn thing?
... and while we are at it, I really wonder what's going on with
that gemfs thing - among the other things, this is the only
user of shmem_file_setup_with_mnt(). Sure, you want your own
options, but that brings another question - is there any reason
for having the huge=... per-superblock rather than per-file?
After all, the readers of ->huge in mm/shmem.c are
mm/shmem.c:582: (shmem_huge == SHMEM_HUGE_FORCE || sbinfo->huge) &&
is_huge_enabled(), sbinfo is an explicit argument
mm/shmem.c:1799:switch (sbinfo->huge) {
shmem_getpage_gfp(), sbinfo comes from inode
mm/shmem.c:2113:if (SHMEM_SB(sb)->huge == SHMEM_HUGE_NEVER)
shmem_get_unmapped_area(), sb comes from file
mm/shmem.c:3531:if (sbinfo->huge)
mm/shmem.c:3532:seq_printf(seq, ",huge=%s",
shmem_format_huge(sbinfo->huge));
->show_options()
mm/shmem.c:3880:switch (sbinfo->huge) {
shmem_huge_enabled(), sbinfo comes from an inode
And the only caller of is_huge_enabled() is shmem_getattr(), with sbinfo
picked from inode.
So is there any reason why the hugepage policy can't be per-file, with
the current being overridable default?
Re: [PATCHv2 2/3] i915: convert to new mount API
On Tue, Aug 06, 2019 at 01:03:06AM +0900, Sergey Senozhatsky wrote: > tmpfs does not set ->remount_fs() anymore and its users need > to be converted to new mount API. Could you explain why the devil do you bother with remount at all? Why not pass the right options when mounting the damn thing?
[PATCHv2 2/3] i915: convert to new mount API
tmpfs does not set ->remount_fs() anymore and its users need
to be converted to new mount API.
BUG: kernel NULL pointer dereference, address:
PF: supervisor instruction fetch in kernel mode
PF: error_code(0x0010) - not-present page
RIP: 0010:0x0
Code: Bad RIP value.
Call Trace:
i915_gemfs_init+0x6e/0xa0 [i915]
i915_gem_init_early+0x76/0x90 [i915]
i915_driver_probe+0x30a/0x1640 [i915]
? kernfs_activate+0x5a/0x80
? kernfs_add_one+0xdd/0x130
pci_device_probe+0x9e/0x110
really_probe+0xce/0x230
driver_probe_device+0x4b/0xc0
device_driver_attach+0x4e/0x60
__driver_attach+0x47/0xb0
? device_driver_attach+0x60/0x60
bus_for_each_dev+0x61/0x90
bus_add_driver+0x167/0x1b0
driver_register+0x67/0xaa
Signed-off-by: Sergey Senozhatsky
Reviewed-by: Chris Wilson
---
drivers/gpu/drm/i915/gem/i915_gemfs.c | 32 +++
1 file changed, 23 insertions(+), 9 deletions(-)
diff --git a/drivers/gpu/drm/i915/gem/i915_gemfs.c
b/drivers/gpu/drm/i915/gem/i915_gemfs.c
index 099f3397aada..feedc9242072 100644
--- a/drivers/gpu/drm/i915/gem/i915_gemfs.c
+++ b/drivers/gpu/drm/i915/gem/i915_gemfs.c
@@ -7,14 +7,17 @@
#include
#include
#include
+#include
#include "i915_drv.h"
#include "i915_gemfs.h"
int i915_gemfs_init(struct drm_i915_private *i915)
{
+ struct fs_context *fc = NULL;
struct file_system_type *type;
struct vfsmount *gemfs;
+ bool ok = true;
type = get_fs_type("tmpfs");
if (!type)
@@ -36,18 +39,29 @@ int i915_gemfs_init(struct drm_i915_private *i915)
struct super_block *sb = gemfs->mnt_sb;
/* FIXME: Disabled until we get W/A for read BW issue. */
char options[] = "huge=never";
- int flags = 0;
- int err;
-
- err = sb->s_op->remount_fs(sb, , options);
- if (err) {
- kern_unmount(gemfs);
- return err;
- }
+
+ ok = false;
+ fc = fs_context_for_reconfigure(sb->s_root, 0, 0);
+ if (IS_ERR(fc))
+ goto out;
+
+ if (!fc->ops->parse_monolithic ||
+ fc->ops->parse_monolithic(fc, options))
+ goto out;
+
+ if (fc->ops->reconfigure && !fc->ops->reconfigure(fc))
+ ok = true;
}
+out:
+ if (!ok)
+ dev_err(i915->drm.dev,
+ "Unable to reconfigure %s. %s\n",
+ "shmemfs for preferred allocation strategy",
+ "Continuing, but performance may suffer");
+ if (!IS_ERR_OR_NULL(fc))
+ put_fs_context(fc);
i915->mm.gemfs = gemfs;
-
return 0;
}
--
2.22.0
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