[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <AANLkTilN3EcYq400ajA2-rf3Xs4MhD-sKCg44fjzKlX1@mail.gmail.com>
Date: Tue, 22 Jun 2010 11:45:45 +0900
From: Minchan Kim <minchan.kim@...il.com>
To: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc: Larry Woodman <lwoodman@...hat.com>, linux-kernel@...r.kernel.org,
linux-mm@...ck.org
Subject: Re: [Patch] Call cond_resched() at bottom of main look in
balance_pgdat()
On Tue, Jun 22, 2010 at 11:24 AM, KOSAKI Motohiro
<kosaki.motohiro@...fujitsu.com> wrote:
>> > =============================================================
>> > Subject: [PATCH] Call cond_resched() at bottom of main look in balance_pgdat()
>> > From: Larry Woodman <lwoodman@...hat.com>
>> >
>> > We are seeing a problem where kswapd gets stuck and hogs the CPU on a
>> > small single CPU system when an OOM kill should occur. When this
>> > happens swap space has been exhausted and the pagecache has been shrunk
>> > to zero. Once kswapd gets the CPU it never gives it up because at least
>> > one zone is below high. Adding a single cond_resched() at the end of
>> > the main loop in balance_pgdat() fixes the problem by allowing the
>> > watchdog and tasks to run and eventually do an OOM kill which frees up
>> > the resources.
>> >
>> > kosaki note: This seems regression caused by commit bb3ab59683
>> > (vmscan: stop kswapd waiting on congestion when the min watermark is
>> > not being met)
>> >
>> > Signed-off-by: Larry Woodman <lwoodman@...hat.com>
>> > Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
>> > ---
>> > mm/vmscan.c | 1 +
>> > 1 files changed, 1 insertions(+), 0 deletions(-)
>> >
>> > diff --git a/mm/vmscan.c b/mm/vmscan.c
>> > index 9c7e57c..c5c46b7 100644
>> > --- a/mm/vmscan.c
>> > +++ b/mm/vmscan.c
>> > @@ -2182,6 +2182,7 @@ loop_again:
>> > */
>> > if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX)
>> > break;
>> > + cond_resched();
>> > }
>> > out:
>> > /*
>> > --
>> > 1.6.5.2
>>
>> Kosaki's patch's goal is that kswap doesn't yield cpu if the zone doesn't meet its
>> min watermark to avoid failing atomic allocation.
>> But this patch could yield kswapd's time slice at any time.
>> Doesn't the patch break your goal in bb3ab59683?
>
> No. it don't break.
>
> Typically, kswapd periodically call shrink_page_list() and it call
> cond_resched() even if bb3ab59683 case.
Hmm. If it is, bb3ab59683 is effective really?
The bb3ab59683's goal is prevent CPU yield in case of free < min_watermark.
But shrink_page_list can yield cpu from kswapd at any time.
So I am not sure what is bb3ab59683's benefit.
Did you have any number about bb3ab59683's effectiveness?
(Of course, I know it's very hard. Just out of curiosity)
As a matter of fact, when I saw this Larry's patch, I thought it would
be better to revert bb3ab59683. Then congestion_wait could yield CPU
to other process.
What do you think about?
--
Kind regards,
Minchan Kim
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists