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Subject[PATCH 06/45] FS-Cache: Recruit a couple of page flags for cache management [ver #41]
Date
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 | 3 ++-
include/linux/page-flags.h | 41 ++++++++++++++++++++++++++++++++++++-----
include/linux/pagemap.h | 14 ++++++++++++++
mm/filemap.c | 18 ++++++++++++++++++
mm/migrate.c | 10 +++++-----
mm/readahead.c | 9 +++++----
mm/swap.c | 4 ++--
mm/swap_state.c | 4 ++--
mm/swapfile.c | 4 ++--
mm/truncate.c | 10 +++++-----
mm/vmscan.c | 6 +++---
11 files changed, 94 insertions(+), 29 deletions(-)

diff --git a/fs/splice.c b/fs/splice.c
index 1abab5c..fd04e95 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -58,7 +58,8 @@ static int page_cache_pipe_buf_steal(struct pipe_inode_info *pipe,
*/
wait_on_page_writeback(page);

- if (PagePrivate(page) && !try_to_release_page(page, GFP_KERNEL))
+ if (page_has_private(page) &&
+ !try_to_release_page(page, GFP_KERNEL))
goto out_unlock;

/*
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 74b9d90..da467b2 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -79,9 +79,11 @@ enum pageflags {
PG_active,
PG_slab,
PG_owner_priv_1, /* Owner use. If pagecache, fs may use*/
+ PG_owner_priv_2, /* Owner use. fs may use in pagecache */
PG_arch_1,
PG_reserved,
PG_private, /* If pagecache, has fs-private data */
+ PG_private_2, /* If pagecache, has fs aux data */
PG_writeback, /* Page is under writeback */
#ifdef CONFIG_PAGEFLAGS_EXTENDED
PG_head, /* A head page */
@@ -106,6 +108,13 @@ enum pageflags {
/* Filesystems */
PG_checked = PG_owner_priv_1,

+ /* Two page bits are conscripted by FS-Cache to maintain local caching state.
+ * These bits are set on pages belonging to the netfs's inodes when those
+ * inodes are being locally cached.
+ */
+ PG_fscache = PG_private_2, /* page backed by cache */
+ PG_fscache_write = PG_owner_priv_2, /* page being written to cache */
+
/* XEN */
PG_pinned = PG_owner_priv_1,
PG_savepinned = PG_dirty,
@@ -192,8 +201,6 @@ PAGEFLAG(Checked, checked) /* Used by some filesystems */
PAGEFLAG(Pinned, pinned) TESTSCFLAG(Pinned, pinned) /* Xen */
PAGEFLAG(SavePinned, savepinned); /* Xen */
PAGEFLAG(Reserved, reserved) __CLEARPAGEFLAG(Reserved, reserved)
-PAGEFLAG(Private, private) __CLEARPAGEFLAG(Private, private)
- __SETPAGEFLAG(Private, private)
PAGEFLAG(SwapBacked, swapbacked) __CLEARPAGEFLAG(SwapBacked, swapbacked)

__PAGEFLAG(SlobPage, slob_page)
@@ -203,6 +210,17 @@ __PAGEFLAG(SlubFrozen, slub_frozen)
__PAGEFLAG(SlubDebug, slub_debug)

/*
+ * Private page markings that may be used by the filesystem that owns the page
+ * for its own purposes.
+ * - PG_private and PG_private_2 cause releasepage() and co to be invoked
+ */
+PAGEFLAG(Private, private) __SETPAGEFLAG(Private, private)
+ __CLEARPAGEFLAG(Private, private)
+PAGEFLAG(Private2, private_2) TESTSCFLAG(Private2, private_2)
+PAGEFLAG(OwnerPriv1, owner_priv_1) TESTCLEARFLAG(OwnerPriv1, owner_priv_1)
+PAGEFLAG(OwnerPriv2, owner_priv_2) TESTSCFLAG(OwnerPriv2, owner_priv_2)
+
+/*
* Only test-and-set exist for PG_writeback. The unconditional operators are
* risky: they bypass page accounting.
*/
@@ -372,9 +390,10 @@ static inline void __ClearPageTail(struct page *page)
#define __PG_MLOCKED 0
#endif

-#define PAGE_FLAGS (1 << PG_lru | 1 << PG_private | 1 << PG_locked | \
- 1 << PG_buddy | 1 << PG_writeback | \
- 1 << PG_slab | 1 << PG_swapcache | 1 << PG_active | \
+#define PAGE_FLAGS (1 << PG_locked | 1 << PG_lru | \
+ 1 << PG_private | 1 << PG_private_2 | \
+ 1 << PG_buddy | 1 << PG_writeback | \
+ 1 << PG_slab | 1 << PG_swapcache | 1 << PG_active | \
__PG_UNEVICTABLE | __PG_MLOCKED)

/*
@@ -399,4 +418,16 @@ static inline void __ClearPageTail(struct page *page)
1 << PG_reserved | 1 << PG_dirty | 1 << PG_swapbacked)

#endif /* !__GENERATING_BOUNDS_H */
+
+/**
+ * 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 709742b..9f51669 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -378,6 +378,20 @@ static inline void wait_on_page_writeback(struct page *page)

extern void end_page_writeback(struct page *page);

+/**
+ * wait_on_page_owner_priv_2 - Wait for PG_owner_priv_2 to become clear
+ * @page: The page to monitor
+ *
+ * Wait for a PG_owner_priv_2 to become clear on the specified page.
+ */
+static inline void wait_on_page_owner_priv_2(struct page *page)
+{
+ if (PageOwnerPriv2(page))
+ wait_on_page_bit(page, PG_owner_priv_2);
+}
+
+extern void end_page_owner_priv_2(struct page *page);
+
/*
* Fault a userspace page into pagetables. Return non-zero on a fault.
*
diff --git a/mm/filemap.c b/mm/filemap.c
index f3e5f89..abfd70c 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -603,6 +603,21 @@ void end_page_writeback(struct page *page)
EXPORT_SYMBOL(end_page_writeback);

/**
+ * end_page_owner_priv_2 - Clear PG_owner_priv_2 and wake up any waiters
+ * @page: the page
+ *
+ * Clear PG_owner_priv_2 and wake up any processes waiting for that event.
+ */
+void end_page_owner_priv_2(struct page *page)
+{
+ if (!TestClearPageOwnerPriv2(page))
+ BUG();
+ smp_mb__after_clear_bit();
+ wake_up_page(page, PG_owner_priv_2);
+}
+EXPORT_SYMBOL(end_page_owner_priv_2);
+
+/**
* __lock_page - get a lock on the page, assuming we need to sleep to get it
* @page: the page to lock
*
@@ -2452,6 +2467,9 @@ EXPORT_SYMBOL(generic_file_aio_write);
* (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 & __GFP_FS).
*
diff --git a/mm/migrate.c b/mm/migrate.c
index 9dd10da..f50093c 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -264,7 +264,7 @@ out:
* The number of remaining references must be:
* 1 for anonymous pages without a mapping
* 2 for pages with a mapping
- * 3 for pages with a mapping and PagePrivate set.
+ * 3 for pages with a mapping and PagePrivate/PagePrivate2 set.
*/
static int migrate_page_move_mapping(struct address_space *mapping,
struct page *newpage, struct page *page)
@@ -284,7 +284,7 @@ static int migrate_page_move_mapping(struct address_space *mapping,
pslot = radix_tree_lookup_slot(&mapping->page_tree,
page_index(page));

- expected_count = 2 + !!PagePrivate(page);
+ expected_count = 2 + !!page_has_private(page);
if (page_count(page) != expected_count ||
(struct page *)radix_tree_deref_slot(pslot) != page) {
spin_unlock_irq(&mapping->tree_lock);
@@ -407,7 +407,7 @@ EXPORT_SYMBOL(fail_migrate_page);

/*
* Common logic to directly migrate a single page suitable for
- * pages that do not use PagePrivate.
+ * pages that do not use PagePrivate/PagePrivate2.
*
* Pages are locked upon entry and exit.
*/
@@ -546,7 +546,7 @@ 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;

@@ -676,7 +676,7 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
* free the metadata, so the page can be freed.
*/
if (!page->mapping) {
- if (!PageAnon(page) && PagePrivate(page)) {
+ if (!PageAnon(page) && page_has_private(page)) {
/*
* Go direct to try_to_free_buffers() here because
* a) that's what try_to_release_page() would do anyway
diff --git a/mm/readahead.c b/mm/readahead.c
index a3366f3..34e8e99 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 2152e48..80bc918 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -478,8 +478,8 @@ void pagevec_strip(struct pagevec *pvec)
for (i = 0; i < pagevec_count(pvec); i++) {
struct page *page = pvec->pages[i];

- if (PagePrivate(page) && trylock_page(page)) {
- if (PagePrivate(page))
+ if (page_has_private(page) && trylock_page(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 3353c90..0c1da6e 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -74,8 +74,8 @@ int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)

BUG_ON(!PageLocked(page));
BUG_ON(PageSwapCache(page));
- BUG_ON(PagePrivate(page));
BUG_ON(!PageSwapBacked(page));
+ BUG_ON(page_has_private(page));
error = radix_tree_preload(gfp_mask);
if (!error) {
page_cache_get(page);
@@ -111,7 +111,7 @@ 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/swapfile.c b/mm/swapfile.c
index 90cb67a..72b8ccc 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -350,7 +350,7 @@ static int remove_exclusive_swap_page_count(struct page *page, int count)
struct swap_info_struct * p;
swp_entry_t entry;

- BUG_ON(PagePrivate(page));
+ BUG_ON(page_has_private(page));
BUG_ON(!PageLocked(page));

if (!PageSwapCache(page))
@@ -432,7 +432,7 @@ void free_swap_and_cache(swp_entry_t entry)
if (page) {
int one_user;

- BUG_ON(PagePrivate(page));
+ BUG_ON(page_has_private(page));
one_user = (page_count(page) == 2);
/* Only cache user (+us), or swap space full? Free it! */
/* Also recheck PageSwapCache after page is locked (above) */
diff --git a/mm/truncate.c b/mm/truncate.c
index 1229211..55206fa 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -50,7 +50,7 @@ void do_invalidatepage(struct page *page, unsigned long offset)
static inline void truncate_partial_page(struct page *page, unsigned partial)
{
zero_user_segment(page, partial, PAGE_CACHE_SIZE);
- if (PagePrivate(page))
+ if (page_has_private(page))
do_invalidatepage(page, partial);
}

@@ -99,7 +99,7 @@ truncate_complete_page(struct address_space *mapping, struct page *page)
if (page->mapping != mapping)
return;

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

cancel_dirty_page(page, PAGE_CACHE_SIZE);
@@ -126,7 +126,7 @@ 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;

clear_page_mlock(page);
@@ -348,7 +348,7 @@ 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;

spin_lock_irq(&mapping->tree_lock);
@@ -356,7 +356,7 @@ invalidate_complete_page2(struct address_space *mapping, struct page *page)
goto failed;

clear_page_mlock(page);
- BUG_ON(PagePrivate(page));
+ BUG_ON(page_has_private(page));
__remove_from_page_cache(page);
spin_unlock_irq(&mapping->tree_lock);
page_cache_release(page); /* pagecache ref */
diff --git a/mm/vmscan.c b/mm/vmscan.c
index c141b3e..44abf78 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -254,7 +254,7 @@ static inline int page_mapping_inuse(struct page *page)

static inline int is_page_cache_freeable(struct page *page)
{
- return page_count(page) - !!PagePrivate(page) == 2;
+ return page_count(page) - !!page_has_private(page) == 2;
}

static int may_write_to_queue(struct backing_dev_info *bdi)
@@ -338,7 +338,7 @@ static pageout_t pageout(struct page *page, struct address_space *mapping,
* Some data journaling orphaned pages can have
* page->mapping == NULL while being dirty with clean buffers.
*/
- if (PagePrivate(page)) {
+ if (page_has_private(page)) {
if (try_to_free_buffers(page)) {
ClearPageDirty(page);
printk("%s: orphaned page\n", __func__);
@@ -708,7 +708,7 @@ 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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