From: James Bottomley <James.Bottomley@HansenPartnership.com> To: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: 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 08:21:51 +0400 [thread overview] Message-ID: <1305519711.4806.7.camel@mulgrave.site> (raw) In-Reply-To: <4DCFAA80.7040109@jp.fujitsu.com> 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. 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. James
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From: James Bottomley <James.Bottomley@HansenPartnership.com> To: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: 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 08:21:51 +0400 [thread overview] Message-ID: <1305519711.4806.7.camel@mulgrave.site> (raw) In-Reply-To: <4DCFAA80.7040109@jp.fujitsu.com> 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. 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. 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>
next prev parent reply other threads:[~2011-05-16 4:22 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 [this message] 2011-05-16 4:21 ` James Bottomley 2011-05-16 5:04 ` Minchan Kim 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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