Re: [PATCH 1/2] mm: prevent to add a page to swap if may_writepage is unset

[Minchan Kim <minchan@kernel.org>]

On Tue, Jan 22, 2013 at 09:09:54AM +0900, Minchan Kim wrote:
> On Mon, Jan 21, 2013 at 09:39:06AM -0500, Rik van Riel wrote:
> > 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 :)
> 
> Thanks, Rik.
> 
> Oops, I missed to Ccing Luigi. Add him again.
> Luigi, Could you test this patch?
> Thanks for your endless effort.
> 
> > 
> > Acked-by: Rik van Riel <riel@redhat.com>
> > 


Andrew,
I hope Luigi confirms this patch but he seems to be very busy.
At a minimum, I tested this patch and passed my test.
Could you apply this and remove [2]?
Otherwise, should I wait for Luigi?

[2] mm: prevent addition of pages to swap if may_writepage is unset