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@xxxxxxxxxx> 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@xxxxxxxxxx>
> > 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@xxxxxxxxxx>
> > Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
> > ---
> > 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@xxxxxxxxxx> 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@xxxxxxxxxx> 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@xxxxxxxxx. For more info on Linux MM,
> >> see: http://www.linux-mm.org/ .
> >> Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
> >
> > --
> > Kind regards,
> > Minchan Kim
>
> --
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--
Kind regards,
Minchan Kim
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