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

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Message-ID: <3939866f-e57e-4caa-919a-558bf6866b82@redhat.com>
Date: Fri, 1 Aug 2025 11:04:00 +0200
From: David Hildenbrand <david@...hat.com>
To: SeongJae Park <sj@...nel.org>, Joshua Hahn <joshua.hahnjy@...il.com>
Cc: 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 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.

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

-- 
Cheers,

David / dhildenb