Messages in this thread | | | Date | Mon, 21 Jan 2013 09:39:06 -0500 | From | Rik van Riel <> | Subject | Re: [PATCH 1/2] mm: prevent to add a page to swap if may_writepage is unset |
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On 01/20/2013 08:52 PM, Minchan Kim wrote:
> From 94086dc7152359d052802c55c82ef19509fe8cce Mon Sep 17 00:00:00 2001 > From: Minchan Kim <minchan@kernel.org> > 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@google.com> > Signed-off-by: Minchan Kim <minchan@kernel.org>
Your patch is a nice simplification. I am ok with the change, provided it works for Luigi :)
Acked-by: Rik van Riel <riel@redhat.com>
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