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: 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>
---
 mm/memory.c   | 19 ++++++++++---------
 mm/swapfile.c |  7 +++++++
 2 files changed, 17 insertions(+), 9 deletions(-)

(limited to 'mm')

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;
-- 
cgit