define page_file_cache() function

Define page_file_cache() function to answer the question:
	is page backed by a file?

Originally part of Rik van Riel's split-lru patch.  Extracted to make
available for other, independent reclaim patches.

Moved inline function to linux/mm_inline.h where it will be needed by
subsequent "split LRU" and "noreclaim" patches.

Unfortunately this needs to use a page flag, since the PG_swapbacked state
needs to be preserved all the way to the point where the page is last
removed from the LRU.  Trying to derive the status from other info in the
page resulted in wrong VM statistics in earlier split VM patchsets.

The total number of page flags in use on a 32 bit machine after this patch
is 19.

[akpm@linux-foundation.org: fix up out-of-order merge fallout]
[hugh@veritas.com: splitlru: shmem_getpage SetPageSwapBacked sooner[
Signed-off-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
Signed-off-by: MinChan Kim <minchan.kim@gmail.com>
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 2 deletions

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index c74d3e875314..57b688cfb5e2 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -93,6 +93,7 @@ enum pageflags {
         PG_mappedtodisk,        /* Has blocks allocated on-disk */
         PG_reclaim,             /* To be reclaimed asap */
         PG_buddy,               /* Page is free, on buddy lists */
+        PG_swapbacked,          /* Page is backed by RAM/swap */
 #ifdef CONFIG_IA64_UNCACHED_ALLOCATOR
         PG_uncached,            /* Page has been mapped as uncached */
 #endif
@@ -176,6 +177,7 @@ 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)
 __PAGEFLAG(SlobFree, slob_free)
@@ -334,7 +336,8 @@ static inline void __ClearPageTail(struct page *page)
  * Flags checked in bad_page().  Pages on the free list should not have
  * these flags set.  It they are, there is a problem.
  */
-#define PAGE_FLAGS_CLEAR_WHEN_BAD (PAGE_FLAGS | 1 << PG_reclaim | 1 << PG_dirty)
+#define PAGE_FLAGS_CLEAR_WHEN_BAD (PAGE_FLAGS | \
+                1 << PG_reclaim | 1 << PG_dirty | 1 << PG_swapbacked)
 
 /*
  * Flags checked when a page is freed.  Pages being freed should not have
@@ -347,7 +350,8 @@ static inline void __ClearPageTail(struct page *page)
  * Pages being prepped should not have these flags set.  It they are, there
  * is a problem.
  */
-#define PAGE_FLAGS_CHECK_AT_PREP (PAGE_FLAGS | 1 << PG_reserved | 1 << PG_dirty)
+#define PAGE_FLAGS_CHECK_AT_PREP (PAGE_FLAGS | \
+                1 << PG_reserved | 1 << PG_dirty | 1 << PG_swapbacked)
 
 #endif /* !__GENERATING_BOUNDS_H */
 #endif  /* PAGE_FLAGS_H */