linux-kernel - 答复: 答复: [PATCH] mm/memcontrol.c: speed up to force empty a memory cgroup

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Date:   Mon, 19 Mar 2018 10:51:42 +0000
From:   "Li,Rongqing" <lirongqing@...du.com>
To:     Michal Hocko <mhocko@...nel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
        "hannes@...xchg.org" <hannes@...xchg.org>,
        "Andrey Ryabinin" <aryabinin@...tuozzo.com>
Subject: 答复: 答复: [PATCH] mm/memcontrol.c: speed up to force empty a memory cgroup



> -----邮件原件-----
> 发件人: Michal Hocko [mailto:mhocko@...nel.org]
> 发送时间: 2018年3月19日 18:38
> 收件人: Li,Rongqing <lirongqing@...du.com>
> 抄送: linux-kernel@...r.kernel.org; linux-mm@...ck.org;
> cgroups@...r.kernel.org; hannes@...xchg.org; Andrey Ryabinin
> <aryabinin@...tuozzo.com>
> 主题: Re: 答复: [PATCH] mm/memcontrol.c: speed up to force empty a
> memory cgroup
> 
> On Mon 19-03-18 10:00:41, Li,Rongqing wrote:
> >
> >
> > > -----邮件原件-----
> > > 发件人: Michal Hocko [mailto:mhocko@...nel.org]
> > > 发送时间: 2018年3月19日 16:54
> > > 收件人: Li,Rongqing <lirongqing@...du.com>
> > > 抄送: linux-kernel@...r.kernel.org; linux-mm@...ck.org;
> > > cgroups@...r.kernel.org; hannes@...xchg.org; Andrey Ryabinin
> > > <aryabinin@...tuozzo.com>
> > > 主题: Re: [PATCH] mm/memcontrol.c: speed up to force empty a
> memory
> > > cgroup
> > >
> > > On Mon 19-03-18 16:29:30, Li RongQing wrote:
> > > > mem_cgroup_force_empty() tries to free only 32
> (SWAP_CLUSTER_MAX)
> > > > pages on each iteration, if a memory cgroup has lots of page
> > > > cache, it will take many iterations to empty all page cache, so
> > > > increase the reclaimed number per iteration to speed it up. same
> > > > as in
> > > > mem_cgroup_resize_limit()
> > > >
> > > > a simple test show:
> > > >
> > > >   $dd if=aaa  of=bbb  bs=1k count=3886080
> > > >   $rm -f bbb
> > > >   $time echo
> 100000000 >/cgroup/memory/test/memory.limit_in_bytes
> > > >
> > > > Before: 0m0.252s ===> after: 0m0.178s
> > >
> > > Andrey was proposing something similar [1]. My main objection was
> > > that his approach might lead to over-reclaim. Your approach is more
> > > conservative because it just increases the batch size. The size is
> > > still rather arbitrary. Same as SWAP_CLUSTER_MAX but that one is a
> > > commonly used unit of reclaim in the MM code.
> > >
> > > I would be really curious about more detailed explanation why having
> > > a larger batch yields to a better performance because we are doingg
> > > SWAP_CLUSTER_MAX batches at the lower reclaim level anyway.
> > >
> >
> > Although SWAP_CLUSTER_MAX is used at the lower level, but the call
> > stack of try_to_free_mem_cgroup_pages is too long, increase the
> > nr_to_reclaim can reduce times of calling
> > function[do_try_to_free_pages, shrink_zones, hrink_node ]
> >
> > mem_cgroup_resize_limit
> > --->try_to_free_mem_cgroup_pages:  .nr_to_reclaim = max(1024,
> > --->SWAP_CLUSTER_MAX),
> >    ---> do_try_to_free_pages
> >      ---> shrink_zones
> >       --->shrink_node
> >        ---> shrink_node_memcg
> >          ---> shrink_list          <-------loop will happen in this place
> [times=1024/32]
> >            ---> shrink_page_list
> 
> Can you actually measure this to be the culprit. Because we should rethink
> our call path if it is too complicated/deep to perform well.
> Adding arbitrary batch sizes doesn't sound like a good way to go to me.

Ok, I will try

-RongQing
> --
> Michal Hocko
> SUSE Labs