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
>
> --
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--
Kind regards,
Minchan Kim
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