From: David Rientjes <rientjes@google.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Satoru Moriya <satoru.moriya@hds.com>,
Andrew Morton <akpm@linux-foundation.org>,
Rik van Riel <riel@redhat.com>,
Randy Dunlap <rdunlap@xenotime.net>,
Satoru Moriya <smoriya@redhat.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
"lwoodman@redhat.com" <lwoodman@redhat.com>,
Seiji Aguchi <saguchi@redhat.com>,
Hugh Dickins <hughd@google.com>,
hannes@cmpxchg.org
Subject: Re: [PATCH -v2 -mm] add extra free kbytes tunable
Date: Thu, 13 Oct 2011 13:55:46 -0700 (PDT) [thread overview]
Message-ID: <alpine.DEB.2.00.1110131351270.24853@chino.kir.corp.google.com> (raw)
In-Reply-To: <20111013143501.a59efa5c.kamezawa.hiroyu@jp.fujitsu.com>
On Thu, 13 Oct 2011, KAMEZAWA Hiroyuki wrote:
> sys_mem_shrink(int nid, int nr_scan_pages, int flags)
>
> This system call scans LRU of specified nodes and free pages on LRU.
> This scan nr_scan_pages in LRU and returns the number of successfully
> freed pages.
> ==
>
> Then, running this progam in SCHED_IDLE, a user can make free pages while
> the system is idle. If running in the highest priority, a user can keep
> free pages as he want. If a user run this under a memcg, user can free
> pages in a memcg.
>
Satoru was specifically talking about the VM using free memory for
pagecache, so doing echo echo 1 > /proc/sys/vm/drop_caches can mitigate
that almost immediately. I think the key to the discussion, though, is
that even the application doesn't know it's bursty memory behavior before
it happens and the kernel entering direct reclaim hurts latency-sensitive
applications.
If there were a change to increase the space significantly between the
high and min watermark when min_free_kbytes changes, that would fix the
problem. The problem is two-fold: that comes at a penalty for systems
or workloads that don't need to reclaim the additional memory, and it's
not clear how much space should exist between those watermarks.
WARNING: multiple messages have this Message-ID (diff)
From: David Rientjes <rientjes@google.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Satoru Moriya <satoru.moriya@hds.com>,
Andrew Morton <akpm@linux-foundation.org>,
Rik van Riel <riel@redhat.com>,
Randy Dunlap <rdunlap@xenotime.net>,
Satoru Moriya <smoriya@redhat.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
"lwoodman@redhat.com" <lwoodman@redhat.com>,
Seiji Aguchi <saguchi@redhat.com>,
Hugh Dickins <hughd@google.com>,
hannes@cmpxchg.org
Subject: Re: [PATCH -v2 -mm] add extra free kbytes tunable
Date: Thu, 13 Oct 2011 13:55:46 -0700 (PDT) [thread overview]
Message-ID: <alpine.DEB.2.00.1110131351270.24853@chino.kir.corp.google.com> (raw)
In-Reply-To: <20111013143501.a59efa5c.kamezawa.hiroyu@jp.fujitsu.com>
On Thu, 13 Oct 2011, KAMEZAWA Hiroyuki wrote:
> sys_mem_shrink(int nid, int nr_scan_pages, int flags)
>
> This system call scans LRU of specified nodes and free pages on LRU.
> This scan nr_scan_pages in LRU and returns the number of successfully
> freed pages.
> ==
>
> Then, running this progam in SCHED_IDLE, a user can make free pages while
> the system is idle. If running in the highest priority, a user can keep
> free pages as he want. If a user run this under a memcg, user can free
> pages in a memcg.
>
Satoru was specifically talking about the VM using free memory for
pagecache, so doing echo echo 1 > /proc/sys/vm/drop_caches can mitigate
that almost immediately. I think the key to the discussion, though, is
that even the application doesn't know it's bursty memory behavior before
it happens and the kernel entering direct reclaim hurts latency-sensitive
applications.
If there were a change to increase the space significantly between the
high and min watermark when min_free_kbytes changes, that would fix the
problem. The problem is two-fold: that comes at a penalty for systems
or workloads that don't need to reclaim the additional memory, and it's
not clear how much space should exist between those watermarks.
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next prev parent reply other threads:[~2011-10-13 20:55 UTC|newest]
Thread overview: 102+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-09-01 14:52 [PATCH -mm] add extra free kbytes tunable Rik van Riel
2011-09-01 14:52 ` Rik van Riel
2011-09-01 17:06 ` Randy Dunlap
2011-09-01 17:06 ` Randy Dunlap
2011-09-01 19:26 ` [PATCH -v2 " Rik van Riel
2011-09-01 19:26 ` Rik van Riel
2011-09-01 21:58 ` Andrew Morton
2011-09-01 21:58 ` Andrew Morton
2011-09-01 22:08 ` David Rientjes
2011-09-01 22:08 ` David Rientjes
2011-09-01 22:16 ` Andrew Morton
2011-09-01 22:16 ` Andrew Morton
2011-09-02 16:31 ` Satoru Moriya
2011-09-02 16:31 ` Satoru Moriya
2011-10-13 7:33 ` Minchan Kim
2011-10-13 7:33 ` Minchan Kim
2011-10-13 8:09 ` KAMEZAWA Hiroyuki
2011-10-13 8:09 ` KAMEZAWA Hiroyuki
[not found] ` <E1FA588BC672D846BDBB452FCA1E308C2389B4@USINDEVS02.corp.hds.com>
2011-09-15 3:33 ` Satoru Moriya
2011-09-15 3:33 ` Satoru Moriya
2011-09-01 22:09 ` Andrew Morton
2011-09-01 22:09 ` Andrew Morton
2011-09-02 16:26 ` [PATCH -mm] fixes & cleanups for "add extra free kbytes tunable" Rik van Riel
2011-09-02 16:26 ` Rik van Riel
2011-09-30 21:43 ` [PATCH -v2 -mm] add extra free kbytes tunable Johannes Weiner
2011-09-30 21:43 ` Johannes Weiner
2011-10-08 3:08 ` David Rientjes
2011-10-08 3:08 ` David Rientjes
2011-10-10 22:37 ` Andrew Morton
2011-10-10 22:37 ` Andrew Morton
2011-10-11 19:32 ` Satoru Moriya
2011-10-11 19:32 ` Satoru Moriya
2011-10-11 19:54 ` Andrew Morton
2011-10-11 19:54 ` Andrew Morton
2011-10-11 20:23 ` Satoru Moriya
2011-10-11 20:23 ` Satoru Moriya
2011-10-11 20:54 ` Andrew Morton
2011-10-11 20:54 ` Andrew Morton
2011-10-12 13:09 ` Rik van Riel
2011-10-12 13:09 ` Rik van Riel
2011-10-12 19:20 ` Andrew Morton
2011-10-12 19:20 ` Andrew Morton
2011-10-12 19:58 ` Rik van Riel
2011-10-12 19:58 ` Rik van Riel
2011-10-12 20:26 ` David Rientjes
2011-10-12 20:26 ` David Rientjes
2011-10-21 23:48 ` Satoru Moriya
2011-10-21 23:48 ` Satoru Moriya
2011-10-23 21:22 ` David Rientjes
2011-10-23 21:22 ` David Rientjes
2011-10-25 2:04 ` Satoru Moriya
2011-10-25 2:04 ` Satoru Moriya
2011-10-25 21:50 ` David Rientjes
2011-10-25 21:50 ` David Rientjes
2011-10-26 18:59 ` Satoru Moriya
2011-10-26 18:59 ` Satoru Moriya
2011-10-12 21:08 ` Satoru Moriya
2011-10-12 21:08 ` Satoru Moriya
2011-10-12 22:41 ` David Rientjes
2011-10-12 22:41 ` David Rientjes
2011-10-12 23:52 ` Satoru Moriya
2011-10-12 23:52 ` Satoru Moriya
2011-10-13 0:01 ` David Rientjes
2011-10-13 0:01 ` David Rientjes
2011-10-13 5:35 ` KAMEZAWA Hiroyuki
2011-10-13 5:35 ` KAMEZAWA Hiroyuki
2011-10-13 20:55 ` David Rientjes [this message]
2011-10-13 20:55 ` David Rientjes
2011-10-14 22:16 ` Satoru Moriya
2011-10-14 22:16 ` Satoru Moriya
2011-10-14 22:46 ` David Rientjes
2011-10-14 22:46 ` David Rientjes
2011-10-14 5:32 ` Satoru Moriya
2011-10-14 5:32 ` Satoru Moriya
2011-10-14 5:06 ` Satoru Moriya
2011-10-14 5:06 ` Satoru Moriya
2011-10-11 23:22 ` David Rientjes
2011-10-11 23:22 ` David Rientjes
2011-10-13 16:54 ` Satoru Moriya
2011-10-13 16:54 ` Satoru Moriya
2011-10-13 20:48 ` David Rientjes
2011-10-13 20:48 ` David Rientjes
2011-10-13 21:11 ` Rik van Riel
2011-10-13 21:11 ` Rik van Riel
2011-10-13 22:02 ` David Rientjes
2011-10-13 22:02 ` David Rientjes
2011-10-11 19:20 ` Satoru Moriya
2011-10-11 19:20 ` Satoru Moriya
2011-10-11 21:04 ` David Rientjes
2011-10-11 21:04 ` David Rientjes
2011-10-12 13:13 ` Rik van Riel
2011-10-12 13:13 ` Rik van Riel
2011-10-12 20:21 ` David Rientjes
2011-10-12 20:21 ` David Rientjes
2011-10-13 4:13 ` Rik van Riel
2011-10-13 4:13 ` Rik van Riel
2011-10-13 5:22 ` David Rientjes
2011-10-13 5:22 ` David Rientjes
2011-10-22 0:11 ` Satoru Moriya
2011-10-22 0:11 ` Satoru Moriya
2011-09-09 23:01 Satoru Moriya
2011-09-09 23:01 ` Satoru Moriya
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