linux-kernel - Re: [PATCH] mm/zswap: Improve with alloc

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Date: Thu, 18 Jan 2024 10:08:09 -0800
From: Nhat Pham <nphamcs@...il.com>
To: Yosry Ahmed <yosryahmed@...gle.com>
Cc: Johannes Weiner <hannes@...xchg.org>, Ronald Monthero <debug.penguin32@...il.com>, sjenning@...hat.com, 
	ddstreet@...e.org, vitaly.wool@...sulko.com, akpm@...ux-foundation.org, 
	chrisl@...nel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/zswap: Improve with alloc_workqueue() call

On Thu, Jan 18, 2024 at 9:03 AM Yosry Ahmed <yosryahmed@...gle.com> wrote:
>
> On Thu, Jan 18, 2024 at 8:48 AM Johannes Weiner <hannes@...xchg.org> wrote:
> >
> > On Thu, Jan 18, 2024 at 11:16:08AM -0500, Johannes Weiner wrote:
> > > > > On Tue, Jan 16, 2024 at 5:32 AM Ronald Monthero
> > > > > > @@ -1620,7 +1620,8 @@ static int zswap_setup(void)
> > > > > >                 zswap_enabled = false;
> > > > > >         }
> > > > > >
> > > > > > -       shrink_wq = create_workqueue("zswap-shrink");
> > > > > > +       shrink_wq = alloc_workqueue("zswap-shrink",
> > > > > > +                       WQ_UNBOUND|WQ_MEM_RECLAIM, 1);
> >
> > > What could make a difference though is the increased concurrency by
> > > switching max_active from 1 to 0. This could cause a higher rate of
> > > shrinker runs, which might increase lock contention and reclaim
> > > volume. That part would be good to double check with the shrinker
> > > benchmarks.
> >
> > Nevermind, I clearly can't read.
>
> Regardless of max_active, we only have one shrink_work per zswap pool,
> and we can only have one instance of the work running at any time,
> right?

I believe so, yeah. Well I guess you can have a weird setup where
somehow multiple pools are full and submit shrink_work concurrently?
But who does that :) But let's just keep it as is to reduce our mental
workload (i.e not having to keep track of what changes) would be
ideal.

>
> >
> > Could still be worthwhile testing with the default 0, but it's not a
> > concern in the patch as-is.
> >
> > Acked-by: Johannes Weiner <hannes@...xchg.org>
> >