linux-kernel - Re: [PATCH 0/5] page reclaim throttle v7

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Date:	Thu, 5 Jun 2008 11:06:37 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	kosaki.motohiro@...fujitsu.com
Cc:	LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 0/5] page reclaim throttle v7

On Thu, 05 Jun 2008 11:12:11 +0900
kosaki.motohiro@...fujitsu.com wrote:

> Hi
> 
> I post latest version of page reclaim patch series.
> 
> This patch is holding up very well under usex stress test
> over 24+ hours :)
> 
> 
> Against: 2.6.26-rc2-mm1
> 
I like this series and I'd like to support this under memcg when
this goes to mainline. (it seems better to test this for a while
before adding some memcg-related changes.)

Then, please give me inputs.
What do you think do I have to do for supporting this in memcg ?
Handling the case of scan_global_lru(sc)==false is enough ?


Thanks,
-Kame


> 
> changelog
> ========================================
>   v6 -> v7
>      o rebase to 2.6.26-rc2-mm1
>      o get_vm_stat: make cpu-unplug safety.
>      o mark vm_max_nr_task_per_zone __read_mostly.
>      o add check __GFP_FS, __GFP_IO for avoid deadlock.
>      o fixed compile error on x86_64.
> 
>   v5 -> v6
>      o rebase to 2.6.25-mm1
>      o use PGFREE statics instead wall time.
>      o separate function type change patch and introduce throttle patch.
> 
>   v4 -> v5
>      o rebase to 2.6.25-rc8-mm1
> 
>   v3 -> v4:
>      o fixed recursive shrink_zone problem.
>      o add last_checked variable in shrink_zone for 
>        prevent corner case regression.
> 
>   v2 -> v3:
>      o use wake_up() instead wake_up_all()
>      o max reclaimers can be changed Kconfig option and sysctl.
>      o some cleanups
> 
>   v1 -> v2:
>      o make per zone throttle 
> 
> 
> 
> background
> =====================================
> current VM implementation doesn't has limit of # of parallel reclaim.
> when heavy workload, it bring to 2 bad things
>   - heavy lock contention
>   - unnecessary swap out
> 
> at end of last year, KAMEZAWA Hiroyuki proposed the patch of page 
> reclaim throttle and explain it improve reclaim time.
> 	http://marc.info/?l=linux-mm&m=119667465917215&w=2
> 
> but unfortunately it works only memcgroup reclaim.
> since, I implement it again for support global reclaim and mesure it.
> 
> 
> benefit
> =====================================
> <<1. fix the bug of incorrect OOM killer>>
> 
> if do following commanc, sometimes OOM killer happened.
> (OOM happend about 10%)
> 
>  $ ./hackbench 125 process 1000
> 
> because following bad scenario is happend.
> 
>    1. memory shortage happend.
>    2. many task call shrink_zone at the same time.
>    3. thus, All page are isolated from LRU at the same time.
>    4. the last task can't isolate any page from LRU.
>    5. it cause reclaim failure.
>    6. it cause OOM killer.
> 
> my patch is directly solution for that problem.
> 
> 
> <<2. performance improvement>>
> I mesure RvR Split LRU series + page reclaim throttle series performance by hackbench.
> 
> result number mean seconds (i.e. smaller is better)
> 
> 
>                                 + split_lru   improvement
>    num_group   2.6.26-rc2-mm1   + throttle    ratio
>    -----------------------------------------------------------------
>    100         28.383           28.247
>    110         31.237           30.83
>    120         33.282           33.473
>    130         36.530           37.356
>    140        101.041           44.873         >200%  
>    150        795.020           96.265         >800%
> 
> 
> Why this patch imrove performance?
> 
> vanilla kernel get unstable performance at swap happend because
> unnecessary swap out happend freqently.
> this patch doesn't improvement best case, but be able to prevent worst case.
> thus, The average performance of hackbench increase largely.
> 
> --
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> 

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