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

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

[Minchan Kim]

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.

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

[Luigi Semenzato]

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.

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>

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

[Minchan Kim]

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

--
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>

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

[Luigi Semenzato]

[-- Attachment #1: Type: text/plain, Size: 9555 bytes --]

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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