linux-kernel - Re: [PATCH] mm, percpu: do not consider sleepable allocations atomic

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Message-ID: <edda21bc-0dfe-4fd9-81e6-705095de9b1b@suse.cz>
Date: Wed, 5 Mar 2025 16:35:07 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Michal Hocko <mhocko@...e.com>
Cc: Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>,
 Filipe Manana <fdmanana@...e.com>, Andrew Morton
 <akpm@...ux-foundation.org>, linux-mm@...ck.org,
 LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm, percpu: do not consider sleepable allocations atomic

On 3/5/25 16:10, Michal Hocko wrote:
> Sorry, I have missed follow ups here.
> 
>> I assume it's probably not easy to
>> implement as page table allocations are involved in the process and we don't
>> have a way to supply preallocated memory for those.
> 
> Why would this be a concern if the allocation is done outside of the
> lock?

It's not a concern if it can be done outside of the lock. I don't know the
code enough to see if it's feasible. There's e.g. pcpu_populate_chunk()
ending up doing vmap_pages_range_noflush() that AFAIK means page table
allocations. Can it be done outside of the lock?