linux-kernel - Re: [PATCH v3] mempolicy: Clarify what zone reclaim means

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Message-ID: <20250806134404.2000234-1-joshua.hahnjy@gmail.com>
Date: Wed,  6 Aug 2025 06:43:52 -0700
From: Joshua Hahn <joshua.hahnjy@...il.com>
To: "Huang, Ying" <ying.huang@...ux.alibaba.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc: David Hildenbrand <david@...hat.com>,
	SeongJae Park <sj@...nel.org>,
	Alistair Popple <apopple@...dia.com>,
	Byungchul Park <byungchul@...com>,
	Gregory Price <gourry@...rry.net>,
	Matthew Brost <matthew.brost@...el.com>,
	Rakie Kim <rakie.kim@...com>,
	Zi Yan <ziy@...dia.com>,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	kernel-team@...a.com
Subject: Re: [PATCH v3] mempolicy: Clarify what zone reclaim means

On Wed, 06 Aug 2025 08:55:42 +0800 "Huang, Ying" <ying.huang@...ux.alibaba.com> wrote:

> Joshua Hahn <joshua.hahnjy@...il.com> writes:
> >
> >  /*
> > + * Enabling zone reclaim means the page allocator will attempt to fulfill
> > + * the allocation request on the current node by triggering reclaim and
> > + * trying to shrink the current node.
> > + * Fallback allocations on the next candidates in the zonelist are considered
> > + * when reclaim fails to free up enough memory in the current node/zone.
> > + *
> >   * These bit locations are exposed in the vm.zone_reclaim_mode sysctl
> > - * ABI.  New bits are OK, but existing bits can never change.
> > + * ABI.  New bits are OK, but existing bits should not be changed.
> 
> Should we avoid to call sysctl ABI here?

Hi Ying,

Makes sense to me as well!

Andrew -- I saw that you added this to mm-unstable yesterday, would you mind
folding the small fixlet below in with it? Please let me know if you would
rather that I send in a new version, whatever works best for you!

As always, thank you for your help : -) Have a great day!


Remove the reference to the vm.zone_reclaim_mode sysctl as an ABI.

Signed-off-by: Joshua Hahn <joshua.hahnjy@...il.com>

diff --git a/include/uapi/linux/mempolicy.h b/include/uapi/linux/mempolicy.h
index 683c130782f0..8fbbe613611a 100644
--- a/include/uapi/linux/mempolicy.h
+++ b/include/uapi/linux/mempolicy.h
@@ -72,8 +72,8 @@ enum {
  * Fallback allocations on the next candidates in the zonelist are considered
  * when reclaim fails to free up enough memory in the current node/zone.
  *
- * These bit locations are exposed in the vm.zone_reclaim_mode sysctl
- * ABI.  New bits are OK, but existing bits should not be changed.
+ * These bit locations are exposed in the vm.zone_reclaim_mode sysctl.
+ * New bits are OK, but existing bits should not be changed.
  */
 #define RECLAIM_ZONE   (1<<0)  /* Enable zone reclaim */
 #define RECLAIM_WRITE  (1<<1)  /* Writeout pages during reclaim */