Re: [PATCH] mm: swap out anonymous page regardless of laptop_mode

[Luigi Semenzato <semenzato@google.com>]

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I'll make sure I use the new version!


On Tue, Jan 8, 2013 at 10:22 PM, Minchan Kim <minchan@kernel.org> wrote:

> Hi Luigi,
>
> On Tue, Jan 08, 2013 at 05:20:25PM -0800, Luigi Semenzato wrote:
> > No problem at all---as I mentioned, we stopped using laptop_mode, so
> > this is no longer an issue for us.
> >
> > I should be able to test the patch for you in the next 2-3 days.  I
> > will let you know if I run into problems.
>
> Right now, I sent new version. I think it's better than this patch.
> Could you test new version instead of this?
>
> Thanks!
>
> >
> > Thanks!
> > Luigi
> >
> > On Mon, Jan 7, 2013 at 11:53 PM, Minchan Kim <minchan@kernel.org> wrote:
> > > Hi Luigi,
> > >
> > > Sorry for really really late response.
> > > Today I have a time to look at this problem and it seems to found the
> problem.
> > > By your help, I can reprocude this problem easily on my KVM machine
> and this
> > > patch solves the problem.
> > >
> > > Could you test below patch? Although this patch is based on recent
> mmotm,
> > > I guess you can apply it easily to 3.4.
> > >
> > > From f74fdf644bec3e7875d245154db953b47b6c9594 Mon Sep 17 00:00:00 2001
> > > From: Minchan Kim <minchan@kernel.org>
> > > Date: Tue, 8 Jan 2013 16:23:31 +0900
> > > Subject: [PATCH] mm: swap out anonymous page regardless of laptop_mode
> > >
> > > 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.
> > >
> > > Luigi reported there was no problem when he disabled laptop_mode.
> > > The problem when I investigate problem is following as.
> > >
> > > try_to_free_pages disable may_writepage if laptop_mode is enabled.
> > > shrink_page_list adds lots of anon pages in swap cache by
> > > add_to_swap, which makes pages Dirty and rotate them to head of
> > > inactive LRU without pageout. If it is repeated, inactive anon LRU
> > > is full of Dirty and SwapCache pages.
> > >
> > > In case of that, isolate_lru_pages fails because it try to isolate
> > > clean page due to may_writepage == 0.
> > >
> > > may_writepage could be 1 only if total_scanned is higher than
> > > writeback_threshold in do_try_to_free_pages but unfortunately,
> > > VM can't isolate anon pages from inactive anon lru list by
> > > above reason and we already reclaimed all file-backed pages.
> > > So it ends up OOM killing.
> > >
> > > This patch makes may_writepage could be set when shrink_inactive_list
> > > encounters SwapCachePage from tail of inactive anon LRU.
> > > What it means that anon LRU list is short and memory pressure
> > > is severe so it would be better to swap out that pages by sacrificing
> > > the power rather than OOM killing.
> > >
> > > Reported-by: Luigi Semenzato <semenzato@google.com>
> > > Signed-off-by: Minchan Kim <minchan@kernel.org>
> > > ---
> > >  mm/vmscan.c |   13 ++++++++++++-
> > >  1 file changed, 12 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > > index ff869d2..7397a6b 100644
> > > --- a/mm/vmscan.c
> > > +++ b/mm/vmscan.c
> > > @@ -1102,7 +1102,7 @@ static unsigned long isolate_lru_pages(unsigned
> long nr_to_scan,
> > >                 prefetchw_prev_lru_page(page, src, flags);
> > >
> > >                 VM_BUG_ON(!PageLRU(page));
> > > -
> > > +retry:
> > >                 switch (__isolate_lru_page(page, mode)) {
> > >                 case 0:
> > >                         nr_pages = hpage_nr_pages(page);
> > > @@ -1112,6 +1112,17 @@ static unsigned long isolate_lru_pages(unsigned
> long nr_to_scan,
> > >                         break;
> > >
> > >                 case -EBUSY:
> > > +                       /*
> > > +                        * If VM encounters PageSwapCache from
> inactive LRU,
> > > +                        * it means we havd to swap out those pages
> regardless
> > > +                        * of laptop_mode for preventing OOM kill.
> > > +                        */
> > > +                       if ((mode & ISOLATE_CLEAN) &&
> PageSwapCache(page) &&
> > > +                               !PageActive(page)) {
> > > +                               mode &= ~ISOLATE_CLEAN;
> > > +                               sc->may_writepage = 1;
> > > +                               goto retry;
> > > +                       }
> > >                         /* else it is being freed elsewhere */
> > >                         list_move(&page->lru, src);
> > >                         continue;
> > > --
> > > 1.7.9.5
> > >
> > >
> > > On Thu, Nov 29, 2012 at 11:31:46AM -0800, Luigi Semenzato wrote:
> > >> Oh well, I found the problem, it's laptop_mode.  We keep it on by
> > >> default.  When I turn it off, I can allocate as fast as I can, and no
> > >> OOMs happen until swap is exhausted.
> > >>
> > >> I don't think this is a desirable behavior even for laptop_mode, so if
> > >> anybody wants to help me debug it (or wants my help in debugging it)
> > >> do let me know.
> > >>
> > >> Thanks!
> > >> Luigi
> > >>
> > >> On Thu, Nov 29, 2012 at 10:46 AM, Luigi Semenzato <
> semenzato@google.com> wrote:
> > >> > Minchan:
> > >> >
> > >> > I tried your suggestion to move the call to wake_all_kswapd from
> after
> > >> > "restart:" to after "rebalance:".  The behavior is still similar,
> but
> > >> > slightly improved.  Here's what I see.
> > >> >
> > >> > Allocating as fast as I can: 1.5 GB of the 3 GB of zram swap are
> used,
> > >> > then OOM kills happen, and the system ends up with 1 GB swap used, 2
> > >> > unused.
> > >> >
> > >> > Allocating 10 MB/s: some kills happen when only 1 to 1.5 GB are
> used,
> > >> > and continue happening while swap fills up.  Eventually swap fills
> up
> > >> > completely.  This is better than before (could not go past about 1
> GB
> > >> > of swap used), but there are too many kills too early.  I would like
> > >> > to see no OOM kills until swap is full or almost full.
> > >> >
> > >> > Allocating 20 MB/s: almost as good as with 10 MB/s, but more kills
> > >> > happen earlier, and not all swap space is used (400 MB free at the
> > >> > end).
> > >> >
> > >> > This is with 200 processes using 20 MB each, and 2:1 compression
> ratio.
> > >> >
> > >> > So it looks like kswapd is still not aggressive enough in pushing
> > >> > pages out.  What's the best way of changing that?  Play around with
> > >> > the watermarks?
> > >> >
> > >> > Incidentally, I also tried removing the min_filelist_kbytes hacky
> > >> > patch, but, as usual, the system thrashes so badly that it's
> > >> > impossible to complete any experiment.  I set it to a lower minimum
> > >> > amount of free file pages, 10 MB instead of the 50 MB which we use
> > >> > normally, and I could run with some thrashing, but I got the same
> > >> > results.
> > >> >
> > >> > Thanks!
> > >> > Luigi
> > >> >
> > >> >
> > >> > On Wed, Nov 28, 2012 at 4:31 PM, Luigi Semenzato <
> semenzato@google.com> wrote:
> > >> >> I am beginning to understand why zram appears to work fine on our
> x86
> > >> >> systems but not on our ARM systems.  The bottom line is that
> swapping
> > >> >> doesn't work as I would expect when allocation is "too fast".
> > >> >>
> > >> >> In one of my tests, opening 50 tabs simultaneously in a Chrome
> browser
> > >> >> on devices with 2 GB of RAM and a zram-disk of 3 GB
> (uncompressed), I
> > >> >> was observing that on the x86 device all of the zram swap space was
> > >> >> used before OOM kills happened, but on the ARM device I would see
> OOM
> > >> >> kills when only about 1 GB (out of 3) was swapped out.
> > >> >>
> > >> >> I wrote a simple program to understand this behavior.  The program
> > >> >> (called "hog") allocates memory and fills it with a mix of
> > >> >> incompressible data (from /dev/urandom) and highly compressible
> data
> > >> >> (1's, just to avoid zero pages) in a given ratio.  The memory is
> never
> > >> >> touched again.
> > >> >>
> > >> >> It turns out that if I don't limit the allocation speed, I see
> > >> >> premature OOM kills also on the x86 device.  If I limit the
> allocation
> > >> >> to 10 MB/s, the premature OOM kills stop happening on the x86
> device,
> > >> >> but still happen on the ARM device.  If I further limit the
> allocation
> > >> >> speed to 5 Mb/s, the premature OOM kills disappear also from the
> ARM
> > >> >> device.
> > >> >>
> > >> >> I have noticed a few time constants in the MM whose value is not
> well
> > >> >> explained, and I am wondering if the code is tuned for some ideal
> > >> >> system that doesn't behave like ours (considering, for instance,
> that
> > >> >> zram is much faster than swapping to a disk device, but it also
> uses
> > >> >> more CPU).  If this is plausible, I am wondering if anybody has
> > >> >> suggestions for changes that I could try out to obtain a better
> > >> >> behavior with a higher allocation speed.
> > >> >>
> > >> >> Thanks!
> > >> >> Luigi
> > >>
> > >> --
> > >> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> > >> the body to majordomo@kvack.org.  For more info on Linux MM,
> > >> see: http://www.linux-mm.org/ .
> > >> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
> > >
> > > --
> > > Kind regards,
> > > Minchan Kim
> >
> > --
> > To unsubscribe, send a message with 'unsubscribe linux-mm' in
> > the body to majordomo@kvack.org.  For more info on Linux MM,
> > see: http://www.linux-mm.org/ .
> > Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
>
> --
> Kind regards,
> Minchan Kim
>

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