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

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Message-ID: <24b4455c-aff9-ca9f-e29f-350833e7a0d1@virtuozzo.com>
Date:   Mon, 6 Dec 2021 16:19:12 +0300
From:   Kirill Tkhai <ktkhai@...tuozzo.com>
To:     David Hildenbrand <david@...hat.com>,
        Michal Hocko <mhocko@...e.com>, Nico Pache <npache@...hat.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 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?