linux-kernel - Re: [RFC PATCH v2 01/10] mm/mremap: introduce more mergeable mremap via MREMAP_RELOCATE

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Message-ID: <dd10778d-3721-44da-8c7d-10d94378777f@lucifer.local>
Date: Sat, 3 May 2025 15:29:08 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Wei Yang <richard.weiyang@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        David Hildenbrand <david@...hat.com>, Pedro Falcato <pfalcato@...e.de>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2 01/10] mm/mremap: introduce more mergeable mremap
 via MREMAP_RELOCATE_ANON

OK have dug into this some more with a drgn script to read actual kernel
metadata state and it's simpler than I thought - the root anon_vma is
self-childed, but descendent anon_vma's are not.

We can correct this with a anon_vma->root == anon_vma check. I believe
we're probably safe with anon_vma reuse, because in that instance the
anon_vma would not be mapped a shared folio.

However, to be safe, I will check this, and I as I said previously, I will
add a number of tests explicitly tested forking scenarios.

The respin should have this fully addressed.

Thanks, Lorenzo