When 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.
Cc: Huang Ying <ying.huang@xxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
---
include/linux/swap.h | 6 ++++++
mm/memory.c | 19 ++++++++++---------
mm/swapfile.c | 7 +++++++
3 files changed, 23 insertions(+), 9 deletions(-)
diff --git a/include/linux/swap.h b/include/linux/swap.h
index cd2f66fdfc2d..1f5c52313890 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -458,6 +458,7 @@ 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 *);
@@ -584,6 +585,11 @@ 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 163ab2062385..aff7e324564f 100644
--- 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 64a3d85226ba..d67715ffc194 100644
--- 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;
--
2.7.4
--
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