mm: swap: SWP_SYNCHRONOUS_IO: skip swapcache only if swapped page has no other reference

When SWP_SYNCHRONOUS_IO swapped-in pages are shared by several
processes, it can cause unnecessary memory wastage by skipping swap
cache.  Because, with swapin fault by read, they could share a page if
the page were in swap cache.  Thus, it avoids allocating same content
new pages.

This patch makes the swapcache skipping work only if the swap pte is
non-sharable.

[akpm@linux-foundation.org: coding-style fixes]
Link: http://lkml.kernel.org/r/1507620825-5537-1-git-send-email-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Ilya Dryomov <idryomov@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Huang Ying <ying.huang@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 32c06f0..8b8a6f9 100644 (file)
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -463,6 +463,7 @@ extern unsigned int count_swap_pages(int, int);
 extern sector_t map_swap_page(struct page *, struct block_device **);
 extern sector_t swapdev_block(int, pgoff_t);
 extern int page_swapcount(struct page *);
+extern int __swap_count(struct swap_info_struct *si, swp_entry_t entry);
 extern int __swp_swapcount(swp_entry_t entry);
 extern int swp_swapcount(swp_entry_t entry);
 extern struct swap_info_struct *page_swap_info(struct page *);
@@ -589,6 +590,11 @@ static inline int page_swapcount(struct page *page)
        return 0;
 }
 
+static inline int __swap_count(struct swap_info_struct *si, swp_entry_t entry)
+{
+       return 0;
+}
+
 static inline int __swp_swapcount(swp_entry_t entry)
 {
        return 0;

diff --git a/mm/memory.c b/mm/memory.c
index f75bff2..a4518ae 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2890,15 +2890,8 @@ int do_swap_page(struct vm_fault *vmf)
        if (!page) {
                struct swap_info_struct *si = swp_swap_info(entry);
 
-               if (!(si->flags & SWP_SYNCHRONOUS_IO)) {
-                       if (vma_readahead)
-                               page = do_swap_page_readahead(entry,
-                                       GFP_HIGHUSER_MOVABLE, vmf, &swap_ra);
-                       else
-                               page = swapin_readahead(entry,
-                                       GFP_HIGHUSER_MOVABLE, vma, vmf->address);
-                       swapcache = page;
-               } else {
+               if (si->flags & SWP_SYNCHRONOUS_IO &&
+                               __swap_count(si, entry) == 1) {
                        /* skip swapcache */
                        page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, vmf->address);
                        if (page) {
@@ -2908,6 +2901,14 @@ int do_swap_page(struct vm_fault *vmf)
                                lru_cache_add_anon(page);
                                swap_readpage(page, true);
                        }
+               } else {
+                       if (vma_readahead)
+                               page = do_swap_page_readahead(entry,
+                                       GFP_HIGHUSER_MOVABLE, vmf, &swap_ra);
+                       else
+                               page = swapin_readahead(entry,
+                                      GFP_HIGHUSER_MOVABLE, vma, vmf->address);
+                       swapcache = page;
                }
 
                if (!page) {

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 85aff8a..3074b02 100644 (file)
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1328,6 +1328,13 @@ int page_swapcount(struct page *page)
        return count;
 }
 
+int __swap_count(struct swap_info_struct *si, swp_entry_t entry)
+{
+       pgoff_t offset = swp_offset(entry);
+
+       return swap_count(si->swap_map[offset]);
+}
+
 static int swap_swapcount(struct swap_info_struct *si, swp_entry_t entry)
 {
        int count = 0;