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

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Message-Id: <20250731224155.1646-1-sj@kernel.org>
Date: Thu, 31 Jul 2025 15:41:55 -0700
From: SeongJae Park <sj@...nel.org>
To: Joshua Hahn <joshua.hahnjy@...il.com>
Cc: SeongJae Park <sj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ying Huang <ying.huang@...ux.alibaba.com>,
	David Hildenbrand <david@...hat.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 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/ ?

> + *
>   * 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)	/* Enable zone reclaim */
>  #define RECLAIM_WRITE	(1<<1)	/* Writeout pages during reclaim */
>  #define RECLAIM_UNMAP	(1<<2)	/* Unmap pages during reclaim */
>  
> 
> base-commit: 260f6f4fda93c8485c8037865c941b42b9cba5d2
> -- 
> 2.47.3
> 

Other than the above trivial thing,

Acked-by: SeongJae Park <sj@...nel.org>


Thanks,
SJ