linux-kernel - Re: [RFC PATCH 2/2] mm/vmscan.c: Prevent allocating shrinker

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Date:   Tue, 7 Dec 2021 16:45:02 -0500
From:   Nico Pache <npache@...hat.com>
To:     Kirill Tkhai <ktkhai@...tuozzo.com>,
        David Hildenbrand <david@...hat.com>,
        Michal Hocko <mhocko@...e.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, shakeelb@...gle.com,
        shy828301@...il.com, guro@...com, vbabka@...e.cz,
        vdavydov.dev@...il.com, raquini@...hat.com
Subject: Re: [RFC PATCH 2/2] mm/vmscan.c: Prevent allocating shrinker_info on
 offlined nodes



On 12/6/21 08:19, Kirill Tkhai wrote:
> On 06.12.2021 13:45, David Hildenbrand wrote:
>>> This doesn't seen complete. Slab shrinkers are used in the reclaim
>>> context. Previously offline nodes could be onlined later and this would
>>> lead to NULL ptr because there is no hook to allocate new shrinker
>>> infos. This would be also really impractical because this would have to
>>> update all existing memcgs...
>>
>> Instead of going through the trouble of updating...
>>
>> ...  maybe just keep for_each_node() and check if the target node is
>> offline. If it's offline, just allocate from the first online node.
>> After all, we're not using __GFP_THISNODE, so there are no guarantees
>> either way ...
> 
> Hm, can't we add shrinker maps allocation to __try_online_node() in addition
> to this patch? 
> 
Thanks for the feedback :) I am currently working a solution similar to this.