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Mon, 28 Jul 2025 09:44:08 +0800 From: "Huang, Ying" To: Joshua Hahn Cc: Andrew Morton , David Hildenbrand , Johannes Weiner , Zi Yan , Matthew Brost , Rakie Kim , Byungchul Park , Gregory Price , Alistair Popple , linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel-team@meta.com Subject: Re: [PATCH] mempolicy: Clarify what RECLAIM_ZONE means In-Reply-To: <20250725173546.2295177-1-joshua.hahnjy@gmail.com> (Joshua Hahn's message of "Fri, 25 Jul 2025 10:35:45 -0700") References: <20250725173546.2295177-1-joshua.hahnjy@gmail.com> Date: Mon, 28 Jul 2025 09:44:06 +0800 Message-ID: <87ms8p2iop.fsf@DESKTOP-5N7EMDA> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii X-Rspamd-Queue-Id: 323EFA0003 X-Stat-Signature: 3nz8gxrc5rskjwpeb19i4iog1qfg6zt8 X-Rspam-User: X-Rspamd-Server: rspam11 X-HE-Tag: 1753667052-606180 X-HE-Meta: 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 29xBQ6J2 7v4AoXSQvy2Rh+D0= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi, Joshua, Joshua Hahn writes: > The zone_reclaim_mode API controls reclaim behavior when a node runs out of > memory. Contrary to its user-facing name, it is internally referred to as > "node_reclaim_mode". This is slightly confusing but there is not much we can > do given that it has already been exposed to userspace (since at least 2.6). > > However, what we can do is to make sure the internal description of what the > bits inside zone_reclaim_mode aligns with what it does in practice. > Setting RECLAIM_ZONE does indeed run shrink_inactive_list, but a more holistic > description would be to explain that zone reclaim modulates whether page > allocation (and khugepaged collapsing) prefers reclaiming & attempting to > allocate locally or should fall back to the next node in the zonelist. > > Change the description to clarify what zone reclaim entails. > > Signed-off-by: Joshua Hahn > --- > include/uapi/linux/mempolicy.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/uapi/linux/mempolicy.h b/include/uapi/linux/mempolicy.h > index 1f9bb10d1a47..24083809d920 100644 > --- a/include/uapi/linux/mempolicy.h > +++ b/include/uapi/linux/mempolicy.h > @@ -69,7 +69,7 @@ enum { > * These bit locations are exposed in the vm.zone_reclaim_mode sysctl > * ABI. New bits are OK, but existing bits can never change. > */ > -#define RECLAIM_ZONE (1<<0) /* Run shrink_inactive_list on the zone */ > +#define RECLAIM_ZONE (1<<0) /* Prefer reclaiming & allocating locally */ > #define RECLAIM_WRITE (1<<1) /* Writeout pages during reclaim */ > #define RECLAIM_UNMAP (1<<2) /* Unmap pages during reclaim */ > > > base-commit: 25fae0b93d1d7ddb25958bcb90c3c0e5e0e202bd Please consider the document of zone_reclaim_mode in Documentation/admin-guide/sysctl/vm.rst too. And, IIUC, RECLAIM_ZONE doesn't mean "locally" exactly. It's legal to bind to some node other than "local node". --- Best Regards, Huang, Ying