linux-kernel - Re: [PATCH] mm/vmscan: when the swappiness is set to 0, memory swapping should be prohibited during the global reclaim process

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Message-ID: <CAN2Y7hxi9VUi=6Yc25hOPkuDyY9Hv++++8L45aVhLmRMXh9+mw@mail.gmail.com>
Date: Fri, 28 Feb 2025 11:18:50 +0800
From: ying chen <yc1082463@...il.com>
To: Johannes Weiner <hannes@...xchg.org>
Cc: Joshua Hahn <joshua.hahnjy@...il.com>, akpm@...ux-foundation.org, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/vmscan: when the swappiness is set to 0, memory
 swapping should be prohibited during the global reclaim process

Got it. Thank you very much.

On Fri, Feb 28, 2025 at 12:19 AM Johannes Weiner <hannes@...xchg.org> wrote:
>
> Hello,
>
> On Thu, Feb 27, 2025 at 07:54:27AM -0800, Joshua Hahn wrote:
> > On Thu, 27 Feb 2025 22:34:51 +0800 ying chen <yc1082463@...il.com> wrote:
>
> > Previously, when the system is under a lot of memory pressure and is
> > facing OOMs, global reclaim can create space for the system and prevent
> > going out of memory by swapping, even when swappiness is 0. If this patch
> > removes that check, it would mean that global reclaim can no longer
> > "bypass" the swappiness == 0 condition.
> >
> > I am also CCing Johannes, who is the original author of this section [1],
> > who clarified in the patch that swappiness == 0 has different meanings for
> > global reclaim and memory cgroup reclaim.
>
> Yes. It's been the behavior for decades that swappiness is merely a
> preference, and that the VM *will* swap to avert OOM. You would break
> users making this change.
>
> If you want to hard-exempt cgroups, set memory.swap.max=0.
>
> [ Yes, it's inconsistent. But it's really cgroup_reclaim() that is the
>   oddball in this. Also for historical reasons... ]
>
> > > when the vm.swappiness is set to 0, global reclaim should also refrain
> > > from memory swapping, just like these cgroups.
> > >
> > > Signed-off-by: yc1082463 <yc1082463@...il.com>
>
> Nacked-by: Johannes Weiner <hannes@...xchg.org>