FS-Cache: Recruit a page flags for cache management

Recruit a page flag to aid in cache management.  The following extra flag is
defined:

 (1) PG_fscache (PG_private_2)

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

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>
Acked-by: Steve Dickson <steved@redhat.com>
Acked-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: Rik van Riel <riel@redhat.com>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Tested-by: Daire Byrne <Daire.Byrne@framestore.com>

8 files changed, 58 insertions, 25 deletions

diff --git a/fs/splice.c b/fs/splice.c
index 4ed0ba44a966..dd727d43e5b7 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -59,7 +59,8 @@ 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 9d99e7471ade..62214c7d2d93 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -82,6 +82,7 @@ enum pageflags {
         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 */
@@ -108,6 +109,12 @@ 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 */
+
         /* XEN */
         PG_pinned = PG_owner_priv_1,
         PG_savepinned = PG_dirty,
@@ -194,8 +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)
@@ -205,6 +210,16 @@ __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)
+
+/*
  * Only test-and-set exist for PG_writeback.  The unconditional operators are
  * risky: they bypass page accounting.
  */
@@ -384,9 +399,10 @@ static inline void __ClearPageTail(struct page *page)
  * these flags set.  It they are, there is a problem.
  */
 #define PAGE_FLAGS_CHECK_AT_FREE \
-        (1 << PG_lru   | 1 << PG_private   | 1 << PG_locked | \
-         1 << PG_buddy | 1 << PG_writeback | 1 << PG_reserved | \
-         1 << PG_slab  | 1 << PG_swapcache | 1 << PG_active | \
+        (1 << PG_lru     | 1 << PG_locked    | \
+         1 << PG_private | 1 << PG_private_2 | \
+         1 << PG_buddy   | 1 << PG_writeback | 1 << PG_reserved | \
+         1 << PG_slab    | 1 << PG_swapcache | 1 << PG_active | \
          __PG_UNEVICTABLE | __PG_MLOCKED)
 
 /*
@@ -397,4 +413,16 @@ static inline void __ClearPageTail(struct page *page)
 #define PAGE_FLAGS_CHECK_AT_PREP        ((1 << NR_PAGEFLAGS) - 1)
 
 #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/mm/filemap.c b/mm/filemap.c
index 126d3973b3d1..cbc5772e7171 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2463,6 +2463,9 @@ 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 a9eff3f092f6..068655d8f883 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -250,7 +250,7 @@ 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)
@@ -270,7 +270,7 @@ 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);
@@ -386,7 +386,7 @@ 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.
  */
@@ -522,7 +522,7 @@ 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;
 
@@ -655,7 +655,7 @@ 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 6be927569cf6..133b6d525513 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -33,14 +33,15 @@ 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 (!trylock_page(page))
                         BUG();
                 page->mapping = mapping;
diff --git a/mm/swap.c b/mm/swap.c
index 6e83084c1f6c..bede23ce64ea 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -448,8 +448,8 @@ 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/truncate.c b/mm/truncate.c
index 1229211104f8..55206fab7b99 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 06e72693b458..425244988bb2 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -283,7 +283,7 @@ 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)
@@ -367,7 +367,7 @@ 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__);
@@ -727,7 +727,7 @@ 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) {