linux-kernel - Re: [PATCH 1/1] mm: fix vma_copy for !CONFIG_PER_VMA

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Message-ID: <0448d4c5-1675-402f-9629-d1348019e38a@redhat.com>
Date: Tue, 10 Dec 2024 10:06:30 +0100
From: David Hildenbrand <david@...hat.com>
To: Suren Baghdasaryan <surenb@...gle.com>, akpm@...ux-foundation.org
Cc: oliver.sang@...el.com, klarasmodin@...il.com, willy@...radead.org,
 liam.howlett@...cle.com, lorenzo.stoakes@...cle.com, mhocko@...e.com,
 vbabka@...e.cz, hannes@...xchg.org, mjguzik@...il.com,
 mgorman@...hsingularity.net, peterx@...hat.com, oleg@...hat.com,
 dave@...olabs.net, paulmck@...nel.org, brauner@...nel.org,
 dhowells@...hat.com, hdanton@...a.com, hughd@...gle.com, minchan@...gle.com,
 jannh@...gle.com, shakeel.butt@...ux.dev, souravpanda@...gle.com,
 pasha.tatashin@...een.com, corbet@....net, linux-doc@...r.kernel.org,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH 1/1] mm: fix vma_copy for !CONFIG_PER_VMA_LOCK

On 09.12.24 23:10, Suren Baghdasaryan wrote:
> vma_copy() function for !CONFIG_PER_VMA_LOCK configuration copies all
> fields using memcpy() as opposed to CONFIG_PER_VMA_LOCK version which
> copies only required fields. anon_vma_chain field should not be copied
> and new vma should instead initialize it to an empty list. Fix this
> by initializing anon_vma_chain inside vma_copy() function. The version
> of vma_copy() for CONFIG_PER_VMA_LOCK is fine since it does not change
> that field and anon_vma_chain of any new vma is already initialized and
> empty.

I'm wondering if there is sufficient reason to have two implementations 
to do the copying.

How expensive would it be to simply use the CONFIG_PER_VMA_LOCK variant 
unconditionally? Is it even measurable in fork() micro-benchmarks?

-- 
Cheers,

David / dhildenb