From aa8d22a11da933dbf880b4933b58931f4aefe91c Mon Sep 17 00:00:00 2001
From: Minchan Kim <minchan@kernel.org>
Date: Wed, 15 Nov 2017 17:33:11 -0800
Subject: [PATCH] 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>
---
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 32c06f028c7b..8b8a6f965785 100644
--- 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 f75bff2cf662..a4518aedf4dd 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 85aff8a42801..3074b02eaa09 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;
--
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