From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-131.freemail.mail.aliyun.com (out30-131.freemail.mail.aliyun.com [115.124.30.131]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E0AA910785 for ; Thu, 31 Jul 2025 01:49:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.131 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753926566; cv=none; b=panlDayheIwWWyTSrU4hpYYNQhzbCiDYlC2bA1nF/l7bwbFAG3gnJ5+Tr9X8lKxGTR2gR6nny2ZUPvWL9or/uDATAb/G+b2CmMJhmxToCCzF54Dy6zrPibWPPApLxgDq4USUq3JKsRLiNv36+5IgjZl0+/Us+VArS/30HWhl6Mg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753926566; c=relaxed/simple; bh=tNPiBujisFHb997GEtpT9Y1QYvcWujeiJOwyNJVXRM4=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=B5TOcsc3IKtPx6nqVlIZiNsXx0DCtDnG7pAuFEFNKP0B4XtjuTzx8q73+Gh5/SBWwh+VG+c+T2iTshckSojS5wYFQONv98Yjnv1tLo9X1i9o1GnjRIgtkTFVrONl79e071gTfsykOW6+HDG/3bB1PPhGbTI/9QpSY0zqhKnjOxI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=iW3lBMCI; arc=none smtp.client-ip=115.124.30.131 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="iW3lBMCI" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1753926556; h=From:To:Subject:Date:Message-ID:MIME-Version:Content-Type; bh=FoVQBKqrO0J50OdfYlBRAT9heWx+qni6PljTTrIPCl4=; b=iW3lBMCIEhMek+VOvbjIDEjTYOw0ONTDHCRWEH0PPO6TpKzfcP5lOyrQ8ival9oZLFvgFTzkQKtJ94IiOhjxL0qQw1+sdOVsrfob8wQMmg6oSx32PnIbCXH1HOlF3He2Hh80wtc+ML2/JJainzcedKXNkImmQkOVJKz+9u+sHqI= Received: from DESKTOP-5N7EMDA(mailfrom:ying.huang@linux.alibaba.com fp:SMTPD_---0WkWQwrt_1753926535 cluster:ay36) by smtp.aliyun-inc.com; Thu, 31 Jul 2025 09:49:14 +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, Dave Hansen Subject: Re: [PATCH] mempolicy: Clarify what RECLAIM_ZONE means In-Reply-To: <20250730201908.2395933-1-joshua.hahnjy@gmail.com> (Joshua Hahn's message of "Wed, 30 Jul 2025 13:19:07 -0700") References: <20250730201908.2395933-1-joshua.hahnjy@gmail.com> Date: Thu, 31 Jul 2025 09:48:54 +0800 Message-ID: <87tt2t9lkp.fsf@DESKTOP-5N7EMDA> User-Agent: Gnus/5.13 (Gnus v5.13) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=ascii Joshua Hahn writes: > On Tue, 29 Jul 2025 08:58:49 +0800 "Huang, Ying" wrote: > >> Joshua Hahn writes: >> >> > On Mon, 28 Jul 2025 09:44:06 +0800 "Huang, Ying" wrote: >> > >> >> 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 >> > >> > Hi Ying, thanks for your review, as always! >> > >> >> Please consider the document of zone_reclaim_mode in >> >> Documentation/admin-guide/sysctl/vm.rst too. >> > >> > Yes, will do. Along with SJ's comment, I think that the information in the >> > admin-guide should be sufficient enough to explain what these bits do, so >> > I think my patch is not very necessary. >> > >> >> And, IIUC, RECLAIM_ZONE doesn't mean "locally" exactly. It's legal to >> >> bind to some node other than "local node". >> > >> > You are correct, it seems you can also reclaim on non-local nodes once you >> > go further down in the zonelist. I think my intent with the new comment was just >> > to indicate a preference to reclaim and allocate on the *current* node, as >> > opposed to falling back to the next node in the zonelist. >> > >> > With that said, I think your comment along with SJ's feedback have gotten me >> > to understand that we proably don't need this change : -) >> >> TBH, I think that it's good to make some change to the comments. >> Because IMHO, the original comments are bound to some specific >> implementation details. Some more general words may be better for the >> user space API description. > > Hi Ying, sorry for the late reply. > > I think that is a good point. Then maybe in that case, we can take SJ's comment > and leave information about both the implementation detail (i.e. that it will > perform shrink inactive_list on the zone), and that it will prefer this over > allocating on the next node as a general description of what happens? Yes. Something like this, or Try to reclaim in the current node/zone before allocating on the fallback. > On that note, one thing that I felt was slightly undercaptured in > Documentation/admin-guide is what "zone reclaim" actually means. What it does > is of course well captured by its name, but it misses the nuance of preferring > reclaim over fallback allocation. > > Actually the whole motivation behind all of this conversation is because I saw > zone reclaim preventing allocation into a second node in a 2-NUMA node system > and was a bit confused until I understood what the implication of having > zone reclaim was. Yes. It's good to improve the document. If it makes you confusing, it may make others confusing too. > Anyways, I can probably spin the patch to include information about what > zone reclaim is, in the comment block above the bits. > > But please feel free to correct me if you feel that the descriptions available > in both the mempolicy.h uapi file or the Documentation/admin-guide is already > enough. Thanks for doing this. --- Best Regards, Huang, Ying