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SubjectRe: [PATCH 10/28] FS-Cache: Recruit a couple of page flags for cache management [try #2]
Date
Nick Piggin <nickpiggin@yahoo.com.au> wrote:

> It is to make everybody happy. Especially in code that everyone works
> on like mm/ and fs/, you can't just have everybody following their own
> slightly different conventions.

Conventions are what people agree they are.

Anyway, I've attached a revised page flags patch if you can take a quick look
over that.

I'll drop the AFS-caching and AFS-write-fix patches for the moment and
concentrate on trying to get FS-Cache working with NFS.

So if we can agree on the two(?) things you brought up with the remaining
patches:

(1) Make PG_fscache overload PG_private_2 rather than PG_owner_priv_2. Would
that make you happy with patch 10 of 28?

(2) Then there's patch 9 of 28 - making read_cache_pages() release private
data that's already attached to pages it then discards due to error. Are
you still going to require that I duplicate read_cache_pages()? Or can
you accept that sharing is sufficient, especially if PG_private_2 now
exists?

David
---
FS-Cache: Recruit a couple of page flags for cache management
From: David Howells <dhowells@redhat.com>

Recruit a couple of page flags to aid in cache management. The following extra
flags are defined:

(1) PG_fscache (PG_private_2)

The marked page is backed by a local cache and is pinning resources in the
cache driver.

(2) PG_fscache_write (PG_owner_priv_2)

The marked page is being written to the local cache. The page may not be
modified whilst this is in progress.

If PG_fscache is set, then things that checked for PG_private will now also
check for that. This includes things like truncation and page invalidation.
The function page_has_private() had been added to make the checks for both
PG_private and PG_private_2 at the same time.

Signed-off-by: David Howells <dhowells@redhat.com>
---
fs/splice.c | 2 +-
include/linux/page-flags.h | 40 ++++++++++++++++++++++++++++++++++++++--
include/linux/pagemap.h | 11 +++++++++++
mm/filemap.c | 16 ++++++++++++++++
mm/migrate.c | 2 +-
mm/page_alloc.c | 3 +++
mm/readahead.c | 9 +++++----
mm/swap.c | 4 ++--
mm/swap_state.c | 4 ++--
mm/truncate.c | 10 +++++-----
mm/vmscan.c | 2 +-
11 files changed, 85 insertions(+), 18 deletions(-)

diff --git a/fs/splice.c b/fs/splice.c
index 6bdcb61..61edad7 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -58,7 +58,7 @@ static int page_cache_pipe_buf_steal(struct pipe_inode_info *pipe,
*/
wait_on_page_writeback(page);

- if (PagePrivate(page))
+ if (page_has_private(page))
try_to_release_page(page, GFP_KERNEL);

/*
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 209d3a4..364f8f9 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -77,25 +77,32 @@
#define PG_active 6
#define PG_slab 7 /* slab debug (Suparna wants this) */

-#define PG_owner_priv_1 8 /* Owner use. If pagecache, fs may use*/
+#define PG_owner_priv_1 8 /* Owner use. fs may use in pagecache */
#define PG_arch_1 9
#define PG_reserved 10
#define PG_private 11 /* If pagecache, has fs-private data */

#define PG_writeback 12 /* Page is under writeback */
+#define PG_private_2 13 /* If pagecache, has fs aux data */
#define PG_compound 14 /* Part of a compound page */
#define PG_swapcache 15 /* Swap page: swp_entry_t in private */

#define PG_mappedtodisk 16 /* Has blocks allocated on-disk */
#define PG_reclaim 17 /* To be reclaimed asap */
+#define PG_owner_priv_2 18 /* Owner use. fs may use in pagecache */
#define PG_buddy 19 /* Page is free, on buddy lists */

/* PG_readahead is only used for file reads; PG_reclaim is only for writes */
#define PG_readahead PG_reclaim /* Reminder to do async read-ahead */

-/* PG_owner_priv_1 users should have descriptive aliases */
+/* PG_owner_priv_1/2 users should have descriptive aliases */
#define PG_checked PG_owner_priv_1 /* Used by some filesystems */
#define PG_pinned PG_owner_priv_1 /* Xen pinned pagetable */
+#define PG_fscache_write PG_owner_priv_2 /* Writing to local cache */
+
+/* PG_private_2 causes releasepage() and co to be invoked */
+#define PG_fscache PG_private_2 /* Backed by local cache */
+

#if (BITS_PER_LONG > 32)
/*
@@ -199,6 +206,24 @@ static inline void SetPageUptodate(struct page *page)
#define TestClearPageWriteback(page) test_and_clear_bit(PG_writeback, \
&(page)->flags)

+#define PageFsCache(page) test_bit(PG_fscache, &(page)->flags)
+#define SetPageFsCache(page) set_bit(PG_fscache, &(page)->flags)
+#define ClearPageFsCache(page) clear_bit(PG_fscache, &(page)->flags)
+#define TestSetPageFsCache(page) test_and_set_bit(PG_fscache, &(page)->flags)
+#define TestClearPageFsCache(page) test_and_clear_bit(PG_fscache, \
+ &(page)->flags)
+
+#define PageFsCacheWrite(page) test_bit(PG_fscache_write, \
+ &(page)->flags)
+#define SetPageFsCacheWrite(page) set_bit(PG_fscache_write, \
+ &(page)->flags)
+#define ClearPageFsCacheWrite(page) clear_bit(PG_fscache_write, \
+ &(page)->flags)
+#define TestSetPageFsCacheWrite(page) test_and_set_bit(PG_fscache_write, \
+ &(page)->flags)
+#define TestClearPageFsCacheWrite(page) test_and_clear_bit(PG_fscache_write, \
+ &(page)->flags)
+
#define PageBuddy(page) test_bit(PG_buddy, &(page)->flags)
#define __SetPageBuddy(page) __set_bit(PG_buddy, &(page)->flags)
#define __ClearPageBuddy(page) __clear_bit(PG_buddy, &(page)->flags)
@@ -272,4 +297,15 @@ static inline void set_page_writeback(struct page *page)
test_set_page_writeback(page);
}

+/**
+ * page_has_private - Determine if page has private stuff
+ * @page: The page to be checked
+ *
+ * Determine if a page has private stuff, indicating that release routines
+ * should be invoked upon it.
+ */
+#define page_has_private(page) \
+ ((page)->flags & ((1 << PG_private) | \
+ (1 << PG_private_2)))
+
#endif /* PAGE_FLAGS_H */
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index db8a410..6a1b317 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -212,6 +212,17 @@ static inline void wait_on_page_writeback(struct page *page)
extern void end_page_writeback(struct page *page);

/*
+ * Wait for a page to finish being written to a local cache
+ */
+static inline void wait_on_page_fscache_write(struct page *page)
+{
+ if (PageFsCacheWrite(page))
+ wait_on_page_bit(page, PG_fscache_write);
+}
+
+extern void end_page_fscache_write(struct page *page);
+
+/*
* Fault a userspace page into pagetables. Return non-zero on a fault.
*
* This assumes that two userspace pages are always sufficient. That's
diff --git a/mm/filemap.c b/mm/filemap.c
index f4d0cde..a86569f 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -572,6 +572,19 @@ void end_page_writeback(struct page *page)
EXPORT_SYMBOL(end_page_writeback);

/**
+ * end_page_fscache_write - End writing page to cache
+ * @page: the page
+ */
+void end_page_fscache_write(struct page *page)
+{
+ if (!TestClearPageFsCacheWrite(page))
+ BUG();
+ smp_mb__after_clear_bit();
+ wake_up_page(page, PG_fscache_write);
+}
+EXPORT_SYMBOL(end_page_fscache_write);
+
+/**
* __lock_page - get a lock on the page, assuming we need to sleep to get it
* @page: the page to lock
*
@@ -2540,6 +2553,9 @@ out:
* (presumably at page->private). If the release was successful, return `1'.
* Otherwise return zero.
*
+ * This may also be called if PG_fscache is set on a page, indicating that the
+ * page is known to the local caching routines.
+ *
* The @gfp_mask argument specifies whether I/O may be performed to release
* this page (__GFP_IO), and whether the call may block (__GFP_WAIT).
*
diff --git a/mm/migrate.c b/mm/migrate.c
index 6a207e8..ebaf557 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -545,7 +545,7 @@ static int fallback_migrate_page(struct address_space *mapping,
* Buffers may be managed in a filesystem specific way.
* We must have no buffers or drop them.
*/
- if (PagePrivate(page) &&
+ if (page_has_private(page) &&
!try_to_release_page(page, GFP_KERNEL))
return -EAGAIN;

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index e1028fa..d0d356b 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -230,6 +230,7 @@ static void bad_page(struct page *page)
dump_stack();
page->flags &= ~(1 << PG_lru |
1 << PG_private |
+ 1 << PG_fscache |
1 << PG_locked |
1 << PG_active |
1 << PG_dirty |
@@ -456,6 +457,7 @@ static inline int free_pages_check(struct page *page)
(page->flags & (
1 << PG_lru |
1 << PG_private |
+ 1 << PG_fscache |
1 << PG_locked |
1 << PG_active |
1 << PG_slab |
@@ -605,6 +607,7 @@ static int prep_new_page(struct page *page, int order, gfp_t gfp_flags)
(page->flags & (
1 << PG_lru |
1 << PG_private |
+ 1 << PG_fscache |
1 << PG_locked |
1 << PG_active |
1 << PG_dirty |
diff --git a/mm/readahead.c b/mm/readahead.c
index 75aa6b6..272ffc7 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -46,14 +46,15 @@ EXPORT_SYMBOL_GPL(file_ra_state_init);

/*
* see if a page needs releasing upon read_cache_pages() failure
- * - the caller of read_cache_pages() may have set PG_private before calling,
- * such as the NFS fs marking pages that are cached locally on disk, thus we
- * need to give the fs a chance to clean up in the event of an error
+ * - the caller of read_cache_pages() may have set PG_private or PG_fscache
+ * before calling, such as the NFS fs marking pages that are cached locally
+ * on disk, thus we need to give the fs a chance to clean up in the event of
+ * an error
*/
static void read_cache_pages_invalidate_page(struct address_space *mapping,
struct page *page)
{
- if (PagePrivate(page)) {
+ if (page_has_private(page)) {
if (TestSetPageLocked(page))
BUG();
page->mapping = mapping;
diff --git a/mm/swap.c b/mm/swap.c
index 9ac8832..22d6e03 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -455,8 +455,8 @@ void pagevec_strip(struct pagevec *pvec)
for (i = 0; i < pagevec_count(pvec); i++) {
struct page *page = pvec->pages[i];

- if (PagePrivate(page) && !TestSetPageLocked(page)) {
- if (PagePrivate(page))
+ if (page_has_private(page) && !TestSetPageLocked(page)) {
+ if (page_has_private(page))
try_to_release_page(page, 0);
unlock_page(page);
}
diff --git a/mm/swap_state.c b/mm/swap_state.c
index b526356..33f1e5c 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -76,7 +76,7 @@ static int __add_to_swap_cache(struct page *page, swp_entry_t entry,

BUG_ON(!PageLocked(page));
BUG_ON(PageSwapCache(page));
- BUG_ON(PagePrivate(page));
+ BUG_ON(page_has_private(page));
error = radix_tree_preload(gfp_mask);
if (!error) {
write_lock_irq(&swapper_space.tree_lock);
@@ -129,7 +129,7 @@ void __delete_from_swap_cache(struct page *page)
BUG_ON(!PageLocked(page));
BUG_ON(!PageSwapCache(page));
BUG_ON(PageWriteback(page));
- BUG_ON(PagePrivate(page));
+ BUG_ON(page_has_private(page));

radix_tree_delete(&swapper_space.page_tree, page_private(page));
set_page_private(page, 0);
diff --git a/mm/truncate.c b/mm/truncate.c
index cadc156..5b7d1c5 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -49,7 +49,7 @@ void do_invalidatepage(struct page *page, unsigned long offset)
static inline void truncate_partial_page(struct page *page, unsigned partial)
{
zero_user_page(page, partial, PAGE_CACHE_SIZE - partial, KM_USER0);
- if (PagePrivate(page))
+ if (page_has_private(page))
do_invalidatepage(page, partial);
}

@@ -100,7 +100,7 @@ truncate_complete_page(struct address_space *mapping, struct page *page)

cancel_dirty_page(page, PAGE_CACHE_SIZE);

- if (PagePrivate(page))
+ if (page_has_private(page))
do_invalidatepage(page, 0);

remove_from_page_cache(page);
@@ -125,7 +125,7 @@ invalidate_complete_page(struct address_space *mapping, struct page *page)
if (page->mapping != mapping)
return 0;

- if (PagePrivate(page) && !try_to_release_page(page, 0))
+ if (page_has_private(page) && !try_to_release_page(page, 0))
return 0;

ret = remove_mapping(mapping, page);
@@ -347,14 +347,14 @@ invalidate_complete_page2(struct address_space *mapping, struct page *page)
if (page->mapping != mapping)
return 0;

- if (PagePrivate(page) && !try_to_release_page(page, GFP_KERNEL))
+ if (page_has_private(page) && !try_to_release_page(page, GFP_KERNEL))
return 0;

write_lock_irq(&mapping->tree_lock);
if (PageDirty(page))
goto failed;

- BUG_ON(PagePrivate(page));
+ BUG_ON(page_has_private(page));
__remove_from_page_cache(page);
write_unlock_irq(&mapping->tree_lock);
ClearPageUptodate(page);
diff --git a/mm/vmscan.c b/mm/vmscan.c
index e5a9597..ff2fa2d 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -578,7 +578,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
* process address space (page_count == 1) it can be freed.
* Otherwise, leave the page on the LRU so it is swappable.
*/
- if (PagePrivate(page)) {
+ if (page_has_private(page)) {
if (!try_to_release_page(page, sc->gfp_mask))
goto activate_locked;
if (!mapping && page_count(page) == 1)

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