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>

1 files changed, 33 insertions, 5 deletions

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 */