Re: [PATCH v10 9/9] fsdax: set a CoW flag when associate reflink mappings
On Tue, Feb 15, 2022 at 6:55 PM Shiyang Ruan wrote:
>
>
>
> 在 2022/2/16 10:09, Dan Williams 写道:
> > On Thu, Jan 27, 2022 at 4:41 AM Shiyang Ruan
> > wrote:
> >>
> >> Introduce a PAGE_MAPPING_DAX_COW flag to support association with CoW file
> >> mappings. In this case, the dax-RMAP already takes the responsibility
> >> to look up for shared files by given dax page. The page->mapping is no
> >> longer to used for rmap but for marking that this dax page is shared.
> >> And to make sure disassociation works fine, we use page->index as
> >> refcount, and clear page->mapping to the initial state when page->index
> >> is decreased to 0.
> >>
> >> With the help of this new flag, it is able to distinguish normal case
> >> and CoW case, and keep the warning in normal case.
> >>
> >> Signed-off-by: Shiyang Ruan
> >> ---
> >> fs/dax.c | 65 --
> >> include/linux/page-flags.h | 6
> >> 2 files changed, 62 insertions(+), 9 deletions(-)
> >>
> >> diff --git a/fs/dax.c b/fs/dax.c
> >> index 250794a5b789..88879c579c1f 100644
> >> --- a/fs/dax.c
> >> +++ b/fs/dax.c
> >> @@ -334,13 +334,46 @@ static unsigned long dax_end_pfn(void *entry)
> >> for (pfn = dax_to_pfn(entry); \
> >> pfn < dax_end_pfn(entry); pfn++)
> >>
> >> +static inline void dax_mapping_set_cow_flag(struct address_space *mapping)
> >> +{
> >> + mapping = (struct address_space *)PAGE_MAPPING_DAX_COW;
> >> +}
> >> +
> >> +static inline bool dax_mapping_is_cow(struct address_space *mapping)
> >> +{
> >> + return (unsigned long)mapping == PAGE_MAPPING_DAX_COW;
> >> +}
> >> +
> >> /*
> >> - * TODO: for reflink+dax we need a way to associate a single page with
> >> - * multiple address_space instances at different linear_page_index()
> >> - * offsets.
> >> + * Set or Update the page->mapping with FS_DAX_MAPPING_COW flag.
> >> + * Return true if it is an Update.
> >> + */
> >> +static inline bool dax_mapping_set_cow(struct page *page)
> >> +{
> >> + if (page->mapping) {
> >> + /* flag already set */
> >> + if (dax_mapping_is_cow(page->mapping))
> >> + return false;
> >> +
> >> + /*
> >> +* This page has been mapped even before it is shared, just
> >> +* need to set this FS_DAX_MAPPING_COW flag.
> >> +*/
> >> + dax_mapping_set_cow_flag(page->mapping);
> >> + return true;
> >> + }
> >> + /* Newly associate CoW mapping */
> >> + dax_mapping_set_cow_flag(page->mapping);
> >> + return false;
> >> +}
> >> +
> >> +/*
> >> + * When it is called in dax_insert_entry(), the cow flag will indicate
> >> that
> >> + * whether this entry is shared by multiple files. If so, set the
> >> page->mapping
> >> + * to be FS_DAX_MAPPING_COW, and use page->index as refcount.
> >>*/
> >> static void dax_associate_entry(void *entry, struct address_space
> >> *mapping,
> >> - struct vm_area_struct *vma, unsigned long address)
> >> + struct vm_area_struct *vma, unsigned long address, bool
> >> cow)
> >> {
> >> unsigned long size = dax_entry_size(entry), pfn, index;
> >> int i = 0;
> >> @@ -352,9 +385,17 @@ static void dax_associate_entry(void *entry, struct
> >> address_space *mapping,
> >> for_each_mapped_pfn(entry, pfn) {
> >> struct page *page = pfn_to_page(pfn);
> >>
> >> - WARN_ON_ONCE(page->mapping);
> >> - page->mapping = mapping;
> >> - page->index = index + i++;
> >> + if (cow) {
> >> + if (dax_mapping_set_cow(page)) {
> >> + /* Was normal, now updated to CoW */
> >> + page->index = 2;
> >> + } else
> >> + page->index++;
> >> + } else {
> >> + WARN_ON_ONCE(page->mapping);
> >> + page->mapping = mapping;
> >> + page->index = index + i++;
> >> + }
> >> }
> >> }
> >>
> >> @@ -370,7 +411,12 @@ static void dax_disassociate_entry(void *entry,
> >> struct address_space *mapping,
> >> struct page *page = pfn_to_page(pfn);
> >>
> >> WARN_ON_ONCE(trunc && page_ref_count(page) > 1);
> >> - WARN_ON_ONCE(page->mapping && page->mapping != mapping);
> >> + if (!dax_mapping_is_cow(page->mapping)) {
> >> + /* keep the CoW flag if this page is still shared
> >> */
> >> + if (page->index-- > 0)
> >> + continue;
> >> + } else
> >> + WARN_ON_ONCE(page->mapping && page->mapping !=
> >> mapping);
> >> page->mapping = NULL;
> >> page->index = 0;
Re: [PATCH v10 9/9] fsdax: set a CoW flag when associate reflink mappings
在 2022/2/16 10:09, Dan Williams 写道:
On Thu, Jan 27, 2022 at 4:41 AM Shiyang Ruan wrote:
Introduce a PAGE_MAPPING_DAX_COW flag to support association with CoW file
mappings. In this case, the dax-RMAP already takes the responsibility
to look up for shared files by given dax page. The page->mapping is no
longer to used for rmap but for marking that this dax page is shared.
And to make sure disassociation works fine, we use page->index as
refcount, and clear page->mapping to the initial state when page->index
is decreased to 0.
With the help of this new flag, it is able to distinguish normal case
and CoW case, and keep the warning in normal case.
Signed-off-by: Shiyang Ruan
---
fs/dax.c | 65 --
include/linux/page-flags.h | 6
2 files changed, 62 insertions(+), 9 deletions(-)
diff --git a/fs/dax.c b/fs/dax.c
index 250794a5b789..88879c579c1f 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -334,13 +334,46 @@ static unsigned long dax_end_pfn(void *entry)
for (pfn = dax_to_pfn(entry); \
pfn < dax_end_pfn(entry); pfn++)
+static inline void dax_mapping_set_cow_flag(struct address_space *mapping)
+{
+ mapping = (struct address_space *)PAGE_MAPPING_DAX_COW;
+}
+
+static inline bool dax_mapping_is_cow(struct address_space *mapping)
+{
+ return (unsigned long)mapping == PAGE_MAPPING_DAX_COW;
+}
+
/*
- * TODO: for reflink+dax we need a way to associate a single page with
- * multiple address_space instances at different linear_page_index()
- * offsets.
+ * Set or Update the page->mapping with FS_DAX_MAPPING_COW flag.
+ * Return true if it is an Update.
+ */
+static inline bool dax_mapping_set_cow(struct page *page)
+{
+ if (page->mapping) {
+ /* flag already set */
+ if (dax_mapping_is_cow(page->mapping))
+ return false;
+
+ /*
+* This page has been mapped even before it is shared, just
+* need to set this FS_DAX_MAPPING_COW flag.
+*/
+ dax_mapping_set_cow_flag(page->mapping);
+ return true;
+ }
+ /* Newly associate CoW mapping */
+ dax_mapping_set_cow_flag(page->mapping);
+ return false;
+}
+
+/*
+ * When it is called in dax_insert_entry(), the cow flag will indicate that
+ * whether this entry is shared by multiple files. If so, set the
page->mapping
+ * to be FS_DAX_MAPPING_COW, and use page->index as refcount.
*/
static void dax_associate_entry(void *entry, struct address_space *mapping,
- struct vm_area_struct *vma, unsigned long address)
+ struct vm_area_struct *vma, unsigned long address, bool cow)
{
unsigned long size = dax_entry_size(entry), pfn, index;
int i = 0;
@@ -352,9 +385,17 @@ static void dax_associate_entry(void *entry, struct
address_space *mapping,
for_each_mapped_pfn(entry, pfn) {
struct page *page = pfn_to_page(pfn);
- WARN_ON_ONCE(page->mapping);
- page->mapping = mapping;
- page->index = index + i++;
+ if (cow) {
+ if (dax_mapping_set_cow(page)) {
+ /* Was normal, now updated to CoW */
+ page->index = 2;
+ } else
+ page->index++;
+ } else {
+ WARN_ON_ONCE(page->mapping);
+ page->mapping = mapping;
+ page->index = index + i++;
+ }
}
}
@@ -370,7 +411,12 @@ static void dax_disassociate_entry(void *entry, struct
address_space *mapping,
struct page *page = pfn_to_page(pfn);
WARN_ON_ONCE(trunc && page_ref_count(page) > 1);
- WARN_ON_ONCE(page->mapping && page->mapping != mapping);
+ if (!dax_mapping_is_cow(page->mapping)) {
+ /* keep the CoW flag if this page is still shared */
+ if (page->index-- > 0)
+ continue;
+ } else
+ WARN_ON_ONCE(page->mapping && page->mapping != mapping);
page->mapping = NULL;
page->index = 0;
}
@@ -810,7 +856,8 @@ static void *dax_insert_entry(struct xa_state *xas,
void *old;
dax_disassociate_entry(entry, mapping, false);
- dax_associate_entry(new_entry, mapping, vmf->vma, vmf->address);
+ dax_associate_entry(new_entry, mapping, vmf->vma, vmf->address,
+ false);
Where is the caller that passes 'true'? Also when that caller arrives
introduce a separate dax_associate_cow_entry() as that's easier to
read than dax_associate_entry(..., true) in case someone does not
remember what that boolean flag means.
This flag is
Re: [PATCH v10 9/9] fsdax: set a CoW flag when associate reflink mappings
On Thu, Jan 27, 2022 at 4:41 AM Shiyang Ruan wrote:
>
> Introduce a PAGE_MAPPING_DAX_COW flag to support association with CoW file
> mappings. In this case, the dax-RMAP already takes the responsibility
> to look up for shared files by given dax page. The page->mapping is no
> longer to used for rmap but for marking that this dax page is shared.
> And to make sure disassociation works fine, we use page->index as
> refcount, and clear page->mapping to the initial state when page->index
> is decreased to 0.
>
> With the help of this new flag, it is able to distinguish normal case
> and CoW case, and keep the warning in normal case.
>
> Signed-off-by: Shiyang Ruan
> ---
> fs/dax.c | 65 --
> include/linux/page-flags.h | 6
> 2 files changed, 62 insertions(+), 9 deletions(-)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index 250794a5b789..88879c579c1f 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -334,13 +334,46 @@ static unsigned long dax_end_pfn(void *entry)
> for (pfn = dax_to_pfn(entry); \
> pfn < dax_end_pfn(entry); pfn++)
>
> +static inline void dax_mapping_set_cow_flag(struct address_space *mapping)
> +{
> + mapping = (struct address_space *)PAGE_MAPPING_DAX_COW;
> +}
> +
> +static inline bool dax_mapping_is_cow(struct address_space *mapping)
> +{
> + return (unsigned long)mapping == PAGE_MAPPING_DAX_COW;
> +}
> +
> /*
> - * TODO: for reflink+dax we need a way to associate a single page with
> - * multiple address_space instances at different linear_page_index()
> - * offsets.
> + * Set or Update the page->mapping with FS_DAX_MAPPING_COW flag.
> + * Return true if it is an Update.
> + */
> +static inline bool dax_mapping_set_cow(struct page *page)
> +{
> + if (page->mapping) {
> + /* flag already set */
> + if (dax_mapping_is_cow(page->mapping))
> + return false;
> +
> + /*
> +* This page has been mapped even before it is shared, just
> +* need to set this FS_DAX_MAPPING_COW flag.
> +*/
> + dax_mapping_set_cow_flag(page->mapping);
> + return true;
> + }
> + /* Newly associate CoW mapping */
> + dax_mapping_set_cow_flag(page->mapping);
> + return false;
> +}
> +
> +/*
> + * When it is called in dax_insert_entry(), the cow flag will indicate that
> + * whether this entry is shared by multiple files. If so, set the
> page->mapping
> + * to be FS_DAX_MAPPING_COW, and use page->index as refcount.
> */
> static void dax_associate_entry(void *entry, struct address_space *mapping,
> - struct vm_area_struct *vma, unsigned long address)
> + struct vm_area_struct *vma, unsigned long address, bool cow)
> {
> unsigned long size = dax_entry_size(entry), pfn, index;
> int i = 0;
> @@ -352,9 +385,17 @@ static void dax_associate_entry(void *entry, struct
> address_space *mapping,
> for_each_mapped_pfn(entry, pfn) {
> struct page *page = pfn_to_page(pfn);
>
> - WARN_ON_ONCE(page->mapping);
> - page->mapping = mapping;
> - page->index = index + i++;
> + if (cow) {
> + if (dax_mapping_set_cow(page)) {
> + /* Was normal, now updated to CoW */
> + page->index = 2;
> + } else
> + page->index++;
> + } else {
> + WARN_ON_ONCE(page->mapping);
> + page->mapping = mapping;
> + page->index = index + i++;
> + }
> }
> }
>
> @@ -370,7 +411,12 @@ static void dax_disassociate_entry(void *entry, struct
> address_space *mapping,
> struct page *page = pfn_to_page(pfn);
>
> WARN_ON_ONCE(trunc && page_ref_count(page) > 1);
> - WARN_ON_ONCE(page->mapping && page->mapping != mapping);
> + if (!dax_mapping_is_cow(page->mapping)) {
> + /* keep the CoW flag if this page is still shared */
> + if (page->index-- > 0)
> + continue;
> + } else
> + WARN_ON_ONCE(page->mapping && page->mapping !=
> mapping);
> page->mapping = NULL;
> page->index = 0;
> }
> @@ -810,7 +856,8 @@ static void *dax_insert_entry(struct xa_state *xas,
> void *old;
>
> dax_disassociate_entry(entry, mapping, false);
> - dax_associate_entry(new_entry, mapping, vmf->vma,
> vmf->address);
> + dax_associate_entry(new_entry, mapping, vmf->vma,
> vmf->address,
> + false);
Where is the caller that passes 'true'? Also when that caller arrives
introduce a sepa
