mm, swap: fix swap readahead marking

In the original implementation, it is possible that the existing pages
in the swap cache (not newly readahead) could be marked as the readahead
pages.  This will cause the statistics of swap readahead be wrong and
influence the swap readahead algorithm too.

This is fixed via marking a page as the readahead page only if it is
newly allocated and read from the disk.

When testing with linpack, after the fixing the swap readahead hit rate
increased from ~66% to ~86%.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: "Huang, Ying" <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Shaohua Li <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Fengguang Wu <[email protected]>
Cc: Tim Chen <[email protected]>
Cc: Dave Hansen <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 11 insertions, 7 deletions

diff --git a/mm/swap_state.c b/mm/swap_state.c
index d1bdb31cab13..a901afe9da61 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -498,7 +498,7 @@ struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
 	unsigned long start_offset, end_offset;
 	unsigned long mask;
 	struct blk_plug plug;
-	bool do_poll = true;
+	bool do_poll = true, page_allocated;
 
 	mask = swapin_nr_pages(offset) - 1;
 	if (!mask)
@@ -514,14 +514,18 @@ struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
 	blk_start_plug(&plug);
 	for (offset = start_offset; offset <= end_offset ; offset++) {
 		/* Ok, do the async read-ahead now */
-		page = read_swap_cache_async(swp_entry(swp_type(entry), offset),
-						gfp_mask, vma, addr, false);
+		page = __read_swap_cache_async(
+			swp_entry(swp_type(entry), offset),
+			gfp_mask, vma, addr, &page_allocated);
 		if (!page)
 			continue;
-		if (offset != entry_offset &&
-		    likely(!PageTransCompound(page))) {
-			SetPageReadahead(page);
-			count_vm_event(SWAP_RA);
+		if (page_allocated) {
+			swap_readpage(page, false);
+			if (offset != entry_offset &&
+			    likely(!PageTransCompound(page))) {
+				SetPageReadahead(page);
+				count_vm_event(SWAP_RA);
+			}
 		}
 		put_page(page);
 	}