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From: Yafang Shao <laoar.shao@gmail.com>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: linux-fsdevel@vger.kernel.org, Linux MM <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Dave Chinner <david@fromorbit.com>,
	Michal Hocko <mhocko@suse.com>, Roman Gushchin <guro@fb.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Kernel Team <kernel-team@fb.com>
Subject: Re: [PATCH] vfs: keep inodes with page cache off the inode shrinker LRU
Date: Thu, 13 Feb 2020 09:47:29 +0800
Message-ID: <CALOAHbCiBqdZzZVC7_c3Um_vDUu9ECsDYUebOL4+=MP9owA_Og@mail.gmail.com> (raw)
In-Reply-To: <20200212164235.GB180867@cmpxchg.org>

On Thu, Feb 13, 2020 at 12:42 AM Johannes Weiner <hannes@cmpxchg.org> wrote:
>
> On Wed, Feb 12, 2020 at 08:25:45PM +0800, Yafang Shao wrote:
> > On Wed, Feb 12, 2020 at 1:55 AM Johannes Weiner <hannes@cmpxchg.org> wrote:
> > > Another variant of this problem was recently observed, where the
> > > kernel violates cgroups' memory.low protection settings and reclaims
> > > page cache way beyond the configured thresholds. It was followed by a
> > > proposal of a modified form of the reverted commit above, that
> > > implements memory.low-sensitive shrinker skipping over populated
> > > inodes on the LRU [1]. However, this proposal continues to run the
> > > risk of attracting disproportionate reclaim pressure to a pool of
> > > still-used inodes,
> >
> > Hi Johannes,
> >
> > If you really think that is a risk, what about bellow additional patch
> > to fix this risk ?
> >
> > diff --git a/fs/inode.c b/fs/inode.c
> > index 80dddbc..61862d9 100644
> > --- a/fs/inode.c
> > +++ b/fs/inode.c
> > @@ -760,7 +760,7 @@ static bool memcg_can_reclaim_inode(struct inode *inode,
> >                 goto out;
> >
> >         cgroup_size = mem_cgroup_size(memcg);
> > -       if (inode->i_data.nrpages + protection >= cgroup_size)
> > +       if (inode->i_data.nrpages)
> >                 reclaimable = false;
> >
> >  out:
> >
> > With this additional patch, we skip all inodes in this memcg until all
> > its page cache pages are reclaimed.
>
> Well that's something we've tried and had to revert because it caused
> issues in slab reclaim. See the History part of my changelog.
>

You misuderstood it.
The reverted patch skips all inodes in the system, while this patch
only works when you turn on memcg.{min, low} protection.
IOW, that is not a default behavior, while it only works when you want
it and only effect your targeted memcg rather than the whole system.

> > > while not addressing the more generic reclaim
> > > inversion problem outside of a very specific cgroup application.
> > >
> >
> > But I have a different understanding.  This method works like a
> > knob. If you really care about your workingset (data), you should
> > turn it on (i.e. by using memcg protection to protect them), while
> > if you don't care about your workingset (data) then you'd better
> > turn it off. That would be more flexible.  Regaring your case in the
> > commit log, why not protect your linux git tree with memcg
> > protection ?
>
> I can't imagine a scenario where I *wouldn't* care about my
> workingset, though. Why should it be opt-in, not the default?

Because the default behavior has caused the XFS performace hit.
(I haven't  checked your patch carefully, so I don't know whehter your
patch fix it yet.)


Thanks

Yafang

  reply index

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-11 17:55 Johannes Weiner
2020-02-11 18:20 ` Johannes Weiner
2020-02-11 19:05 ` Rik van Riel
2020-02-11 19:31   ` Johannes Weiner
2020-02-11 23:44     ` Andrew Morton
2020-02-12  0:28       ` Linus Torvalds
2020-02-12  0:47         ` Andrew Morton
2020-02-12  1:03           ` Linus Torvalds
2020-02-12  8:50             ` Russell King - ARM Linux admin
2020-02-13  9:50               ` Lucas Stach
2020-02-13 16:52               ` Arnd Bergmann
2020-02-15 11:25                 ` Geert Uytterhoeven
2020-02-15 16:59                   ` Arnd Bergmann
2020-02-16  9:44                     ` Geert Uytterhoeven
2020-02-16 19:54                       ` Chris Paterson
2020-02-16 20:38                         ` Arnd Bergmann
2020-02-20 14:35                           ` Chris Paterson
2020-02-26 18:04                 ` santosh.shilimkar
2020-02-26 21:01                   ` Arnd Bergmann
2020-02-26 21:11                     ` santosh.shilimkar
2020-03-06 20:34                       ` Nishanth Menon
2020-03-07  1:08                         ` santosh.shilimkar
2020-03-08 10:58                         ` Arnd Bergmann
2020-03-08 14:19                           ` Russell King - ARM Linux admin
2020-03-09 13:33                             ` Arnd Bergmann
2020-03-09 14:04                               ` Russell King - ARM Linux admin
2020-03-09 15:04                                 ` Arnd Bergmann
2020-03-10  9:16                                   ` Michal Hocko
2020-03-09 15:59                           ` Catalin Marinas
2020-03-09 16:09                             ` Russell King - ARM Linux admin
2020-03-09 16:57                               ` Catalin Marinas
2020-03-09 19:46                               ` Arnd Bergmann
2020-03-11 14:29                                 ` Catalin Marinas
2020-03-11 16:59                                   ` Arnd Bergmann
2020-03-11 17:26                                     ` Catalin Marinas
2020-03-11 22:21                                       ` Arnd Bergmann
2020-02-12  3:58         ` Matthew Wilcox
2020-02-12  8:09         ` Michal Hocko
2020-02-17 13:31         ` Pavel Machek
2020-02-12 16:35       ` Johannes Weiner
2020-02-12 18:26         ` Andrew Morton
2020-02-12 18:52           ` Johannes Weiner
2020-02-12 12:25 ` Yafang Shao
2020-02-12 16:42   ` Johannes Weiner
2020-02-13  1:47     ` Yafang Shao [this message]
2020-02-13 13:46       ` Johannes Weiner
2020-02-14  2:02         ` Yafang Shao
2020-02-13 18:34 ` [PATCH v2] " Johannes Weiner
2020-02-14 16:53 ` [PATCH] " kbuild test robot
2020-02-14 21:30 ` kbuild test robot
2020-02-14 21:30 ` [PATCH] vfs: fix boolreturn.cocci warnings kbuild test robot

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