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Thu, 27 Feb 2025 19:19:01 -0800 (PST) MIME-Version: 1.0 References: <20250227155431.2534325-1-joshua.hahnjy@gmail.com> <20250227161934.GA115948@cmpxchg.org> In-Reply-To: <20250227161934.GA115948@cmpxchg.org> From: ying chen Date: Fri, 28 Feb 2025 11:18:50 +0800 X-Gm-Features: AQ5f1Joh0aVbw7xiYVJ0kWKptPeL2p-x3jXiRWW-DQKziIHJqYrQ9XLsJvcdjV4 Message-ID: Subject: Re: [PATCH] mm/vmscan: when the swappiness is set to 0, memory swapping should be prohibited during the global reclaim process To: Johannes Weiner Cc: Joshua Hahn , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: 55k7rp3mqsf3iknkddsyxhuyzhwz7raw X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: B66D680006 X-Rspam-User: X-HE-Tag: 1740712743-477790 X-HE-Meta: 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 2eqXxEsL 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.125815, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Got it. Thank you very much. On Fri, Feb 28, 2025 at 12:19=E2=80=AFAM Johannes Weiner 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 wrot= e: > > > 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 pat= ch > > removes that check, it would mean that global reclaim can no longer > > "bypass" the swappiness =3D=3D 0 condition. > > > > I am also CCing Johannes, who is the original author of this section [1= ], > > who clarified in the patch that swappiness =3D=3D 0 has different meani= ngs 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=3D0. > > [ 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 refrai= n > > > from memory swapping, just like these cgroups. > > > > > > Signed-off-by: yc1082463 > > Nacked-by: Johannes Weiner