[Devel] [PATCH RHEL7 COMMIT] ms/vmscan: fix increasing nr_isolated incurred by putback unevictable pages

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-514.26.1.vz7.33.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-514.26.1.vz7.33.6
------>
commit 7df75aaf78f00e8759ebea070470a44dd4ade20d
Author: Jaewon Kim <jaewon31.kim at samsung.com>
Date:   Thu Jul 13 19:40:42 2017 +0400

    ms/vmscan: fix increasing nr_isolated incurred by putback unevictable pages
    
    commit c54839a722a02818677bcabe57e957f0ce4f841d upstream.
    
    reclaim_clean_pages_from_list() assumes that shrink_page_list() returns
    number of pages removed from the candidate list.  But shrink_page_list()
    puts back mlocked pages without passing it to caller and without
    counting as nr_reclaimed.  This increases nr_isolated.
    
    To fix this, this patch changes shrink_page_list() to pass unevictable
    pages back to caller.  Caller will take care those pages.
    
    Minchan said:
    
    It fixes two issues.
    
    1. With unevictable page, cma_alloc will be successful.
    
    Exactly speaking, cma_alloc of current kernel will fail due to
    unevictable pages.
    
    2. fix leaking of NR_ISOLATED counter of vmstat
    
    With it, too_many_isolated works.  Otherwise, it could make hang until
    the process get SIGKILL.
    
    Signed-off-by: Jaewon Kim <jaewon31.kim at samsung.com>
    Acked-by: Minchan Kim <minchan at kernel.org>
    Cc: Mel Gorman <mgorman at techsingularity.net>
    Acked-by: Vlastimil Babka <vbabka at suse.cz>
    Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
    Signed-off-by: Jiri Slaby <jslaby at suse.cz>
    
    Applied in the scope of
    https://jira.sw.ru/browse/PSBM-68029
    
    Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 mm/vmscan.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 1b4471e..7b24537 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1147,7 +1147,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 		if (PageSwapCache(page))
 			try_to_free_swap(page);
 		unlock_page(page);
-		putback_lru_page(page);
+		list_add(&page->lru, &ret_pages);
 		continue;
 
 activate_locked: