mm: Use owner_priv bit for PageSwapCache, valid when PageSwapBacked

A page is not added to the swap cache without being swap backed,
so PageSwapBacked mappings can use PG_owner_priv_1 for PageSwapCache.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Bob Peterson <rpeterso@redhat.com>
Cc: Steven Whitehouse <swhiteho@redhat.com>
Cc: Andrew Lutomirski <luto@kernel.org>
Cc: Andreas Gruenbacher <agruenba@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 16 insertions, 9 deletions

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 74e4dda91238..a57c909a15e4 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -87,7 +87,6 @@ enum pageflags {
         PG_private_2,           /* If pagecache, has fs aux data */
         PG_writeback,           /* Page is under writeback */
         PG_head,                /* A head page */
-        PG_swapcache,           /* Swap page: swp_entry_t in private */
         PG_mappedtodisk,        /* Has blocks allocated on-disk */
         PG_reclaim,             /* To be reclaimed asap */
         PG_swapbacked,          /* Page is backed by RAM/swap */
@@ -110,6 +109,9 @@ enum pageflags {
         /* Filesystems */
         PG_checked = PG_owner_priv_1,
 
+        /* SwapBacked */
+        PG_swapcache = PG_owner_priv_1, /* Swap page: swp_entry_t in private */
+
         /* 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.
@@ -314,7 +316,13 @@ PAGEFLAG_FALSE(HighMem)
 #endif
 
 #ifdef CONFIG_SWAP
-PAGEFLAG(SwapCache, swapcache, PF_NO_COMPOUND)
+static __always_inline int PageSwapCache(struct page *page)
+{
+        return PageSwapBacked(page) && test_bit(PG_swapcache, &page->flags);
+
+}
+SETPAGEFLAG(SwapCache, swapcache, PF_NO_COMPOUND)
+CLEARPAGEFLAG(SwapCache, swapcache, PF_NO_COMPOUND)
 #else
 PAGEFLAG_FALSE(SwapCache)
 #endif
@@ -701,12 +709,12 @@ static inline void ClearPageSlabPfmemalloc(struct page *page)
  * Flags checked when a page is freed.  Pages being freed should not have
  * these flags set.  It they are, there is a problem.
  */
-#define PAGE_FLAGS_CHECK_AT_FREE \
-        (1UL << PG_lru   | 1UL << PG_locked    | \
-         1UL << PG_private | 1UL << PG_private_2 | \
-         1UL << PG_writeback | 1UL << PG_reserved | \
-         1UL << PG_slab  | 1UL << PG_swapcache | 1UL << PG_active | \
-         1UL << PG_unevictable | __PG_MLOCKED)
+#define PAGE_FLAGS_CHECK_AT_FREE                                \
+        (1UL << PG_lru          | 1UL << PG_locked      |       \
+         1UL << PG_private      | 1UL << PG_private_2   |       \
+         1UL << PG_writeback    | 1UL << PG_reserved    |       \
+         1UL << PG_slab         | 1UL << PG_active      |       \
+         1UL << PG_unevictable  | __PG_MLOCKED)
 
 /*
  * Flags checked when a page is prepped for return by the page allocator.
diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h
index 5a81ab48a2fb..30c2adbdebe8 100644
--- a/include/trace/events/mmflags.h
+++ b/include/trace/events/mmflags.h
@@ -95,7 +95,6 @@
         {1UL << PG_private_2,           "private_2"     },              \
         {1UL << PG_writeback,           "writeback"     },              \
         {1UL << PG_head,                "head"          },              \
-        {1UL << PG_swapcache,           "swapcache"     },              \
         {1UL << PG_mappedtodisk,        "mappedtodisk"  },              \
         {1UL << PG_reclaim,             "reclaim"       },              \
         {1UL << PG_swapbacked,          "swapbacked"    },              \