linux-kernel - Re: [PATCH v3 1/2] mm: zswap: fix global shrinker memcg iteration

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Message-ID: <CAKEwX=OpNXsR7FTBq2J8pwusnAOOCvEXuATLvHFMMT1DDt9kog@mail.gmail.com>
Date: Tue, 23 Jul 2024 08:55:05 -0700
From: Nhat Pham <nphamcs@...il.com>
To: Takero Funaki <flintglass@...il.com>
Cc: Johannes Weiner <hannes@...xchg.org>, Yosry Ahmed <yosryahmed@...gle.com>, 
	Chengming Zhou <chengming.zhou@...ux.dev>, Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] mm: zswap: fix global shrinker memcg iteration

On Tue, Jul 23, 2024 at 8:35 AM Takero Funaki <flintglass@...il.com> wrote:
>
> 2024年7月23日(火) 6:39 Nhat Pham <nphamcs@...il.com>:
> >
> > On Fri, Jul 19, 2024 at 9:41 PM Takero Funaki <flintglass@...il.com> wrote:
> > >
> > > This patch fixes an issue where the zswap global shrinker stopped
> > > iterating through the memcg tree.
> > >
> > > The problem was that shrink_worker() would stop iterating when a memcg
> > > was being offlined and restart from the tree root.  Now, it properly
> > > handles the offline memcg and continues shrinking with the next memcg.
> > >
> > > To avoid holding refcount of offline memcg encountered during the memcg
> > > tree walking, shrink_worker() must continue iterating to release the
> > > offline memcg to ensure the next memcg stored in the cursor is online.
> > >
> > > The offline memcg cleaner has also been changed to avoid the same issue.
> > > When the next memcg of the offlined memcg is also offline, the refcount
> > > stored in the iteration cursor was held until the next shrink_worker()
> > > run. The cleaner must release the offline memcg recursively.
> > >
> > > Fixes: a65b0e7607cc ("zswap: make shrinking memcg-aware")
> > > Signed-off-by: Takero Funaki <flintglass@...il.com>
> > Hmm LGTM for the most part - a couple nits
> > [...]
> > > +                       zswap_next_shrink = mem_cgroup_iter(NULL,
> > > +                                       zswap_next_shrink, NULL);
> > nit: this can fit in a single line right? Looks like it's exactly 80 characters.
>
> Isn't that over 90 chars? But yes, we can reduce line breaks using
> memcg as temporary, like:

Huh. Weird. I applied the patch locally, and it looked 80 chars to me ha.

Anyway - just some nits. If checkpatch complains then yeah no need to fix this.