linux-kernel - Re: [PATCH v2] mempolicy: Clarify what zone reclaim means

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Message-ID: <20250801145037.2078591-1-joshua.hahnjy@gmail.com>
Date: Fri,  1 Aug 2025 07:50:30 -0700
From: Joshua Hahn <joshua.hahnjy@...il.com>
To: David Hildenbrand <david@...hat.com>
Cc: SeongJae Park <sj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ying Huang <ying.huang@...ux.alibaba.com>,
	Zi Yan <ziy@...dia.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Matthew Brost <matthew.brost@...el.com>,
	Rakie Kim <rakie.kim@...com>,
	Byungchul Park <byungchul@...com>,
	Gregory Price <gourry@...rry.net>,
	Alistair Popple <apopple@...dia.com>,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	kernel-team@...a.com
Subject: Re: [PATCH v2] mempolicy: Clarify what zone reclaim means

On Fri, 1 Aug 2025 11:04:00 +0200 David Hildenbrand <david@...hat.com> wrote:

> On 01.08.25 00:41, SeongJae Park wrote:
> > On Thu, 31 Jul 2025 14:07:37 -0700 Joshua Hahn <joshua.hahnjy@...il.com> wrote:
> > 
> >> The zone_reclaim_mode API controls the 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 can be confusing. But because we cannot change the name of the API since
> >> it has been in place since at least 2.6, let's try to be more explicit about
> >> what the behavior of this API is.
> >>
> >> Change the description to clarify what zone reclaim entails, and be explicit
> >> about the RECLAIM_ZONE bit, whose purpose has led to some confusion in the
> >> past already [1] [2].
> >>
> >> [1] https://lore.kernel.org/linux-mm/1579005573-58923-1-git-send-email-alex.shi@linux.alibaba.com/
> >> [2] https://lore.kernel.org/linux-mm/20200626003459.D8E015CA@viggo.jf.intel.com/
> >>
> >> Signed-off-by: Joshua Hahn <joshua.hahnjy@...il.com>
> >> ---
> >>   include/uapi/linux/mempolicy.h | 8 +++++++-
> >>   1 file changed, 7 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/include/uapi/linux/mempolicy.h b/include/uapi/linux/mempolicy.h
> >> index 1f9bb10d1a47..6c9c9385ff89 100644
> >> --- a/include/uapi/linux/mempolicy.h
> >> +++ b/include/uapi/linux/mempolicy.h
> >> @@ -66,10 +66,16 @@ enum {
> >>   #define MPOL_F_MORON	(1 << 4) /* Migrate On protnone Reference On Node */
> >>   
> >>   /*
> >> + * 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
> >> + * zone when reclaim fails to free up enough memory in the current node/zone.
> > 
> > s/zone when reclaim fails/when reclaim fails/ ?
> 
> Agreed, that confused me as well.

Hi David, hi SJ!

Thank you both for catching this, I definitely missed this before sending the
patch out. Will fix in the next version!

> Acked-by: David Hildenbrand <david@...hat.com>

And thank you for your Ack : -) Have a great day!
Joshua

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