On 01/20/2013 08:52 PM, Minchan Kim wrote:
From 94086dc7152359d052802c55c82ef19509fe8cce Mon Sep 17 00:00:00 2001
From: Minchan Kim <minchan@xxxxxxxxxx>
Date: Mon, 21 Jan 2013 10:43:43 +0900
Subject: [PATCH] mm: Use up free swap space before reaching OOM kill
Recently, Luigi reported there are lots of free swap space when
OOM happens. It's easily reproduced on zram-over-swap, where
many instance of memory hogs are running and laptop_mode is enabled.
He said there was no problem when he disabled laptop_mode.
The problem when I investigate problem is following as.
Assumption for easy explanation: There are no page cache page in system
because they all are already reclaimed.
1. try_to_free_pages disable may_writepage when laptop_mode is enabled.
2. shrink_inactive_list isolates victim pages from inactive anon lru list.
3. shrink_page_list adds them to swapcache via add_to_swap but it doesn't
pageout because sc->may_writepage is 0 so the page is rotated back into
inactive anon lru list. The add_to_swap made the page Dirty by SetPageDirty.
4. 3 couldn't reclaim any pages so do_try_to_free_pages increase priority and
retry reclaim with higher priority.
5. shrink_inactlive_list try to isolate victim pages from inactive anon lru list
but got failed because it try to isolate pages with ISOLATE_CLEAN mode but
inactive anon lru list is full of dirty pages by 3 so it just returns
without any reclaim progress.
6. do_try_to_free_pages doesn't set may_writepage due to zero total_scanned.
Because sc->nr_scanned is increased by shrink_page_list but we don't call
shrink_page_list in 5 due to short of isolated pages.
Above loop is continued until OOM happens.
The problem didn't happen before [1] was merged because old logic's
isolatation in shrink_inactive_list was successful and tried to call
shrink_page_list to pageout them but it still ends up failed to page out
by may_writepage. But important point is that sc->nr_scanned was increased
although we couldn't swap out them so do_try_to_free_pages could set
may_writepages.
Since [1] was introduced, it's not a good idea any more to depends on
only the number of scanned pages for setting may_writepage. So this patch
adds new trigger point of setting may_writepage as below DEF_PRIOIRTY - 2
which is used to show the significant memory pressure in VM so it's good
fit for our purpose which would be better to lose power saving or clickety
rather than OOM killing.
[1] f80c067[mm: zone_reclaim: make isolate_lru_page() filter-aware]
Reported-by: Luigi Semenzato <semenzato@xxxxxxxxxx>
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
Your patch is a nice simplification. I am ok with the
change, provided it works for Luigi :)
Acked-by: Rik van Riel <riel@xxxxxxxxxx>
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