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From: Minchan Kim <minchan.kim@gmail.com>
To: James Bottomley <James.Bottomley@hansenpartnership.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
	mgorman@suse.de, akpm@linux-foundation.org,
	colin.king@canonical.com, raghu.prabhu13@gmail.com, jack@suse.cz,
	chris.mason@oracle.com, cl@linux.com, penberg@kernel.org,
	riel@redhat.com, hannes@cmpxchg.org,
	linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, linux-ext4@vger.kernel.org
Subject: Re: [PATCH 4/4] mm: vmscan: If kswapd has been running too long, allow it to sleep
Date: Mon, 16 May 2011 14:04:00 +0900	[thread overview]
Message-ID: <BANLkTi=oe4Ties6awwhHFPf42EXCn2U4MQ@mail.gmail.com> (raw)
In-Reply-To: <1305519711.4806.7.camel@mulgrave.site>

On Mon, May 16, 2011 at 1:21 PM, James Bottomley
<James.Bottomley@hansenpartnership.com> wrote:
> On Sun, 2011-05-15 at 19:27 +0900, KOSAKI Motohiro wrote:
>> (2011/05/13 23:03), Mel Gorman wrote:
>> > Under constant allocation pressure, kswapd can be in the situation where
>> > sleeping_prematurely() will always return true even if kswapd has been
>> > running a long time. Check if kswapd needs to be scheduled.
>> >
>> > Signed-off-by: Mel Gorman<mgorman@suse.de>
>> > ---
>> >   mm/vmscan.c |    4 ++++
>> >   1 files changed, 4 insertions(+), 0 deletions(-)
>> >
>> > diff --git a/mm/vmscan.c b/mm/vmscan.c
>> > index af24d1e..4d24828 100644
>> > --- a/mm/vmscan.c
>> > +++ b/mm/vmscan.c
>> > @@ -2251,6 +2251,10 @@ static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining,
>> >     unsigned long balanced = 0;
>> >     bool all_zones_ok = true;
>> >
>> > +   /* If kswapd has been running too long, just sleep */
>> > +   if (need_resched())
>> > +           return false;
>> > +
>>
>> Hmm... I don't like this patch so much. because this code does
>>
>> - don't sleep if kswapd got context switch at shrink_inactive_list
>
> This isn't entirely true:  need_resched() will be false, so we'll follow
> the normal path for determining whether to sleep or not, in effect
> leaving the current behaviour unchanged.
>
>> - sleep if kswapd didn't
>
> This also isn't entirely true: whether need_resched() is true at this
> point depends on a whole lot more that whether we did a context switch
> in shrink_inactive. It mostly depends on how long we've been running
> without giving up the CPU.  Generally that will mean we've been round
> the shrinker loop hundreds to thousands of times without sleeping.
>
>> It seems to be semi random behavior.
>
> Well, we have to do something.  Chris Mason first suspected the hang was
> a kswapd rescheduling problem a while ago.  We tried putting
> cond_rescheds() in several places in the vmscan code, but to no avail.

Is it a result of  test with patch of Hannes(ie, !pgdat_balanced)?

If it isn't, it would be nop regardless of putting cond_reshed at vmscan.c.
Because, although we complete zone balancing, kswapd doesn't sleep as
pgdat_balance returns wrong result. And at last VM calls
balance_pgdat. In this case, balance_pgdat returns without any work as
kswap couldn't find zones which have not enough free pages and goto
out. kswapd could repeat this work infinitely. So you don't have a
chance to call cond_resched.

But if your test was with Hanne's patch, I am very curious how come
kswapd consumes CPU a lot.

> The need_resched() in sleeping_prematurely() seems to be about the best
> option.  The other option might be just to put a cond_resched() in
> kswapd_try_to_sleep(), but that will really have about the same effect.

I don't oppose it but before that, I think we have to know why kswapd
consumes CPU a lot although we applied Hannes' patch.

>
> James
>
>
> --
> 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/ .
> Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
>



-- 
Kind regards,
Minchan Kim

WARNING: multiple messages have this Message-ID (diff)
From: Minchan Kim <minchan.kim@gmail.com>
To: James Bottomley <James.Bottomley@hansenpartnership.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
	mgorman@suse.de, akpm@linux-foundation.org,
	colin.king@canonical.com, raghu.prabhu13@gmail.com, jack@suse.cz,
	chris.mason@oracle.com, cl@linux.com, penberg@kernel.org,
	riel@redhat.com, hannes@cmpxchg.org,
	linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, linux-ext4@vger.kernel.org
Subject: Re: [PATCH 4/4] mm: vmscan: If kswapd has been running too long, allow it to sleep
Date: Mon, 16 May 2011 14:04:00 +0900	[thread overview]
Message-ID: <BANLkTi=oe4Ties6awwhHFPf42EXCn2U4MQ@mail.gmail.com> (raw)
In-Reply-To: <1305519711.4806.7.camel@mulgrave.site>

On Mon, May 16, 2011 at 1:21 PM, James Bottomley
<James.Bottomley@hansenpartnership.com> wrote:
> On Sun, 2011-05-15 at 19:27 +0900, KOSAKI Motohiro wrote:
>> (2011/05/13 23:03), Mel Gorman wrote:
>> > Under constant allocation pressure, kswapd can be in the situation where
>> > sleeping_prematurely() will always return true even if kswapd has been
>> > running a long time. Check if kswapd needs to be scheduled.
>> >
>> > Signed-off-by: Mel Gorman<mgorman@suse.de>
>> > ---
>> >   mm/vmscan.c |    4 ++++
>> >   1 files changed, 4 insertions(+), 0 deletions(-)
>> >
>> > diff --git a/mm/vmscan.c b/mm/vmscan.c
>> > index af24d1e..4d24828 100644
>> > --- a/mm/vmscan.c
>> > +++ b/mm/vmscan.c
>> > @@ -2251,6 +2251,10 @@ static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining,
>> >     unsigned long balanced = 0;
>> >     bool all_zones_ok = true;
>> >
>> > +   /* If kswapd has been running too long, just sleep */
>> > +   if (need_resched())
>> > +           return false;
>> > +
>>
>> Hmm... I don't like this patch so much. because this code does
>>
>> - don't sleep if kswapd got context switch at shrink_inactive_list
>
> This isn't entirely true:  need_resched() will be false, so we'll follow
> the normal path for determining whether to sleep or not, in effect
> leaving the current behaviour unchanged.
>
>> - sleep if kswapd didn't
>
> This also isn't entirely true: whether need_resched() is true at this
> point depends on a whole lot more that whether we did a context switch
> in shrink_inactive. It mostly depends on how long we've been running
> without giving up the CPU.  Generally that will mean we've been round
> the shrinker loop hundreds to thousands of times without sleeping.
>
>> It seems to be semi random behavior.
>
> Well, we have to do something.  Chris Mason first suspected the hang was
> a kswapd rescheduling problem a while ago.  We tried putting
> cond_rescheds() in several places in the vmscan code, but to no avail.

Is it a result of  test with patch of Hannes(ie, !pgdat_balanced)?

If it isn't, it would be nop regardless of putting cond_reshed at vmscan.c.
Because, although we complete zone balancing, kswapd doesn't sleep as
pgdat_balance returns wrong result. And at last VM calls
balance_pgdat. In this case, balance_pgdat returns without any work as
kswap couldn't find zones which have not enough free pages and goto
out. kswapd could repeat this work infinitely. So you don't have a
chance to call cond_resched.

But if your test was with Hanne's patch, I am very curious how come
kswapd consumes CPU a lot.

> The need_resched() in sleeping_prematurely() seems to be about the best
> option.  The other option might be just to put a cond_resched() in
> kswapd_try_to_sleep(), but that will really have about the same effect.

I don't oppose it but before that, I think we have to know why kswapd
consumes CPU a lot although we applied Hannes' patch.

>
> James
>
>
> --
> 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/ .
> Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
> 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/ .
Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

  reply	other threads:[~2011-05-16  5:04 UTC|newest]

Thread overview: 119+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-05-13 14:03 [PATCH 0/4] Reduce impact to overall system of SLUB using high-order allocations V2 Mel Gorman
2011-05-13 14:03 ` Mel Gorman
2011-05-13 14:03 ` [PATCH 1/4] mm: vmscan: Correct use of pgdat_balanced in sleeping_prematurely Mel Gorman
2011-05-13 14:03   ` Mel Gorman
2011-05-13 14:28   ` Johannes Weiner
2011-05-13 14:28     ` Johannes Weiner
2011-05-14 16:30   ` Minchan Kim
2011-05-14 16:30     ` Minchan Kim
2011-05-16 14:30   ` Rik van Riel
2011-05-16 14:30     ` Rik van Riel
2011-05-13 14:03 ` [PATCH 2/4] mm: slub: Do not wake kswapd for SLUBs speculative high-order allocations Mel Gorman
2011-05-13 14:03   ` Mel Gorman
2011-05-16 21:10   ` David Rientjes
2011-05-16 21:10     ` David Rientjes
2011-05-18  6:09     ` Pekka Enberg
2011-05-18  6:09       ` Pekka Enberg
2011-05-18 17:21       ` Christoph Lameter
2011-05-18 17:21         ` Christoph Lameter
2011-05-13 14:03 ` [PATCH 3/4] mm: slub: Do not take expensive steps " Mel Gorman
2011-05-13 14:03   ` Mel Gorman
2011-05-16 21:16   ` David Rientjes
2011-05-16 21:16     ` David Rientjes
2011-05-17  8:42     ` Mel Gorman
2011-05-17  8:42       ` Mel Gorman
2011-05-17 13:51       ` Christoph Lameter
2011-05-17 13:51         ` Christoph Lameter
2011-05-17 16:22         ` Mel Gorman
2011-05-17 16:22           ` Mel Gorman
2011-05-17 17:52           ` Christoph Lameter
2011-05-17 17:52             ` Christoph Lameter
2011-05-17 19:35             ` David Rientjes
2011-05-17 19:35               ` David Rientjes
2011-05-17 19:31       ` David Rientjes
2011-05-17 19:31         ` David Rientjes
2011-05-13 14:03 ` [PATCH 4/4] mm: vmscan: If kswapd has been running too long, allow it to sleep Mel Gorman
2011-05-13 14:03   ` Mel Gorman
2011-05-15 10:27   ` KOSAKI Motohiro
2011-05-15 10:27     ` KOSAKI Motohiro
2011-05-16  4:21     ` James Bottomley
2011-05-16  4:21       ` James Bottomley
2011-05-16  5:04       ` Minchan Kim [this message]
2011-05-16  5:04         ` Minchan Kim
2011-05-16  8:45         ` Mel Gorman
2011-05-16  8:45           ` Mel Gorman
2011-05-16  8:45           ` Mel Gorman
2011-05-16  8:58           ` Minchan Kim
2011-05-16  8:58             ` Minchan Kim
2011-05-16  8:58             ` Minchan Kim
2011-05-16 10:27             ` Mel Gorman
2011-05-16 10:27               ` Mel Gorman
2011-05-16 10:27               ` Mel Gorman
2011-05-16 23:50               ` Minchan Kim
2011-05-16 23:50                 ` Minchan Kim
2011-05-17  0:48                 ` Minchan Kim
2011-05-17  0:48                   ` Minchan Kim
2011-05-17  0:48                   ` Minchan Kim
2011-05-17 10:38                 ` Mel Gorman
2011-05-17 10:38                   ` Mel Gorman
2011-05-17 10:38                   ` Mel Gorman
2011-05-17 13:50                   ` Colin Ian King
2011-05-17 13:50                     ` Colin Ian King
2011-05-17 16:15                     ` [PATCH] mm: vmscan: Correctly check if reclaimer should schedule during shrink_slab Mel Gorman
2011-05-17 16:15                       ` Mel Gorman
2011-05-18  0:45                       ` KOSAKI Motohiro
2011-05-18  0:45                         ` KOSAKI Motohiro
2011-05-19  0:03                       ` Minchan Kim
2011-05-19  0:03                         ` Minchan Kim
2011-05-19  0:03                         ` Minchan Kim
2011-05-19  0:09                       ` Minchan Kim
2011-05-19  0:09                         ` Minchan Kim
2011-05-19  0:09                         ` Minchan Kim
2011-05-19 11:36                         ` Colin Ian King
2011-05-19 11:36                           ` Colin Ian King
2011-05-20  0:06                           ` Minchan Kim
2011-05-20  0:06                             ` Minchan Kim
2011-05-20  0:06                             ` Minchan Kim
2011-05-18  4:19                     ` [PATCH 4/4] mm: vmscan: If kswapd has been running too long, allow it to sleep Minchan Kim
2011-05-18  4:19                       ` Minchan Kim
2011-05-18  7:39                       ` Colin Ian King
2011-05-18  7:39                         ` Colin Ian King
2011-05-18  4:09                   ` James Bottomley
2011-05-18  4:09                     ` James Bottomley
2011-05-18  1:05                 ` KOSAKI Motohiro
2011-05-18  1:05                   ` KOSAKI Motohiro
2011-05-18  5:44                   ` Minchan Kim
2011-05-18  5:44                     ` Minchan Kim
2011-05-18  5:44                     ` Minchan Kim
2011-05-18  6:05                     ` KOSAKI Motohiro
2011-05-18  6:05                       ` KOSAKI Motohiro
2011-05-18  9:58                     ` Mel Gorman
2011-05-18  9:58                       ` Mel Gorman
2011-05-18  9:58                       ` Mel Gorman
2011-05-18 22:55                       ` Minchan Kim
2011-05-18 22:55                         ` Minchan Kim
2011-05-18 23:54                         ` KOSAKI Motohiro
2011-05-18 23:54                           ` KOSAKI Motohiro
2011-05-18  0:26               ` KOSAKI Motohiro
2011-05-18  0:26                 ` KOSAKI Motohiro
2011-05-18  9:57                 ` Mel Gorman
2011-05-18  9:57                   ` Mel Gorman
2011-05-16  8:45     ` Mel Gorman
2011-05-16  8:45       ` Mel Gorman
2011-05-16 14:30   ` Rik van Riel
2011-05-16 14:30     ` Rik van Riel
2011-05-13 15:19 ` [PATCH 0/4] Reduce impact to overall system of SLUB using high-order allocations V2 James Bottomley
2011-05-13 15:19   ` James Bottomley
2011-05-13 15:19   ` James Bottomley
2011-05-13 15:52   ` Mel Gorman
2011-05-13 15:52     ` Mel Gorman
2011-05-13 15:21 ` Christoph Lameter
2011-05-13 15:21   ` Christoph Lameter
2011-05-13 15:43   ` Mel Gorman
2011-05-13 15:43     ` Mel Gorman
2011-05-14  8:34 ` Colin Ian King
2011-05-14  8:34   ` Colin Ian King
2011-05-16  8:37   ` Mel Gorman
2011-05-16  8:37     ` Mel Gorman
2011-05-16 11:24     ` Colin Ian King
2011-05-16 11:24       ` Colin Ian King

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