linux-kernel - Re: [PATCH v3] mm: memcg: Use larger batches for proactive reclaim

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Message-ID: <CABdmKX0-nWU4P7ZJqOMusRCuhewf+kg1x==U7m52=MaKeRCYWg@mail.gmail.com>
Date: Mon, 19 Feb 2024 08:39:19 -0800
From: "T.J. Mercier" <tjmercier@...gle.com>
To: Michal Hocko <mhocko@...e.com>
Cc: Johannes Weiner <hannes@...xchg.org>, Roman Gushchin <roman.gushchin@...ux.dev>, 
	Shakeel Butt <shakeelb@...gle.com>, Muchun Song <muchun.song@...ux.dev>, 
	Andrew Morton <akpm@...ux-foundation.org>, Efly Young <yangyifei03@...ishou.com>, 
	android-mm@...gle.com, yuzhao@...gle.com, mkoutny@...e.com, 
	Yosry Ahmed <yosryahmed@...gle.com>, cgroups@...r.kernel.org, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] mm: memcg: Use larger batches for proactive reclaim

On Mon, Feb 19, 2024 at 4:11 AM Michal Hocko <mhocko@...e.com> wrote:
>
> On Tue 06-02-24 09:58:41, Michal Hocko wrote:
> > On Mon 05-02-24 20:01:40, T.J. Mercier wrote:
> > > On Mon, Feb 5, 2024 at 1:16 PM Michal Hocko <mhocko@...e.com> wrote:
> > > >
> > > > On Mon 05-02-24 12:47:47, T.J. Mercier wrote:
> > > > > On Mon, Feb 5, 2024 at 12:36 PM Michal Hocko <mhocko@...ecom> wrote:
> > > > [...]
> > > > > > This of something like
> > > > > > timeout $TIMEOUT echo $TARGET > $MEMCG_PATH/memory.reclaim
> > > > > > where timeout acts as a stop gap if the reclaim cannot finish in
> > > > > > TIMEOUT.
> > > > >
> > > > > Yeah I get the desired behavior, but using sc->nr_reclaimed to achieve
> > > > > it is what's bothering me.
> > > >
> > > > I am not really happy about this subtlety. If we have a better way then
> > > > let's do it. Better in its own patch, though.
> > > >
> > > > > It's already wired up that way though, so if you want to make this
> > > > > change now then I can try to test for the difference using really
> > > > > large reclaim targets.
> > > >
> > > > Yes, please. If you want it a separate patch then no objection from me
> > > > of course. If you do no like the nr_to_reclaim bailout then maybe we can
> > > > go with a simple break out flag in scan_control.
> > > >
> > > > Thanks!
> > >
> > > It's a bit difficult to test under the too_many_isolated check, so I
> > > moved the fatal_signal_pending check outside and tried with that.
> > > Performing full reclaim on the /uid_0 cgroup with a 250ms delay before
> > > SIGKILL, I got an average of 16ms better latency with
> > > sc->nr_to_reclaim across 20 runs ignoring one 1s outlier with
> > > SWAP_CLUSTER_MAX.
> >
> > This will obviously scale with the number of memcgs in the hierarchy but
> > you are right that too_many_isolated makes the whole fatal_signal_pending
> > check rather inefficient. I haven't missed that. The reclaim path is
> > rather convoluted so this will likely be more complex than I
> > anticipated. I will think about that some more.
> >
> > In order to not delay your patch, please repost with suggested updates
> > to the changelog. This needs addressing IMO but I do not think this is
> > critical at this stage.
>
> Has there been a new version or a proposal to refine the changelog
> posted?

Hi Michal,

I updated the commit message in V4 to include a sentence about restart
cost, and added a line above each reclaim test to note the MGLRU
config and whether the memcg LRU was used or not.

https://lore.kernel.org/all/20240206175251.3364296-1-tjmercier@google.com/

> --
> Michal Hocko
> SUSE Labs