linux-kernel - Re: [PATCH v2] mm: memcg: Use larger batches for proactive reclaim

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Date: Fri, 2 Feb 2024 14:51:24 -0800
From: "T.J. Mercier" <tjmercier@...gle.com>
To: Johannes Weiner <hannes@...xchg.org>
Cc: Yosry Ahmed <yosryahmed@...gle.com>, Michal Hocko <mhocko@...nel.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, cgroups@...r.kernel.org, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm: memcg: Use larger batches for proactive reclaim

On Fri, Feb 2, 2024 at 2:41 PM Johannes Weiner <hannes@...xchg.org> wrote:
>
> On Fri, Feb 02, 2024 at 02:13:20PM -0800, Yosry Ahmed wrote:
> > On Fri, Feb 2, 2024 at 2:10 PM T.J. Mercier <tjmercier@...gle.com> wrote:
> > > @@ -6965,6 +6965,9 @@ static ssize_t memory_reclaim(struct kernfs_open_file *of, char *buf,
> > >         while (nr_reclaimed < nr_to_reclaim) {
> > >                 unsigned long reclaimed;
> > >
> > > +               /* Will converge on zero, but reclaim enforces a minimum */
> > > +               unsigned long batch_size = (nr_to_reclaim - nr_reclaimed) / 4;
> > > +
> > >                 if (signal_pending(current))
> > >                         return -EINTR;
> > >
> > > @@ -6977,7 +6980,7 @@ static ssize_t memory_reclaim(struct kernfs_open_file *of, char *buf,
> > >                         lru_add_drain_all();
> > >
> > >                 reclaimed = try_to_free_mem_cgroup_pages(memcg,
> > > -                                       min(nr_to_reclaim - nr_reclaimed, SWAP_CLUSTER_MAX),
> > > +                                       batch_size,
> > >                                         GFP_KERNEL, reclaim_options);
> >
> > I think the above two lines should now fit into one.
>
> Yeah might as well compact that again. The newline in the declarations
> is a bit unusual for this codebase as well, and puts the comment sort
> of away from the "reclaim" it refers to. This?
>
>                 /* Will converge on zero, but reclaim enforces a minimum */
>                 batch_size = (nr_to_reclaim - nr_reclaimed) / 4;
>
>                 reclaimed = try_to_free_mem_cgroup_pages(memcg, batch_size,
>                                         GFP_KERNEL, reclaim_options);
>
> But agreed, it's all just nitpickety nickpicking. :)
>
> Acked-by: Johannes Weiner <hannes@...xchg.org>

-std=gnu11 to the rescue

+               /* Will converge on zero, but reclaim enforces a minimum */
+               unsigned long batch_size = (nr_to_reclaim - nr_reclaimed) / 4;
                reclaimed = try_to_free_mem_cgroup_pages(memcg,
-                                       min(nr_to_reclaim -
nr_reclaimed, SWAP_CLUSTER_MAX),
+                                       batch_size,
                                        GFP_KERNEL, reclaim_options);