linux-kernel - Re: [PATCH 0/2] make VM_SOFTDIRTY a sticky VMA flag

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Message-ID: <6c0f29f6-5d6c-457d-a5b7-9bdede35d4f7@lucifer.local>
Date: Wed, 19 Nov 2025 17:21:16 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Cyrill Gorcunov <gorcunov@...il.com>
Cc: Andrei Vagin <avagin@...il.com>, Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...nel.org>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
        Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
        Jann Horn <jannh@...gle.com>, Pedro Falcato <pfalcato@...e.de>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org, criu@...ts.linux.dev
Subject: Re: [PATCH 0/2] make VM_SOFTDIRTY a sticky VMA flag

On Wed, Nov 19, 2025 at 04:09:49PM +0300, Cyrill Gorcunov wrote:
> On Mon, Nov 17, 2025 at 07:57:30PM +0000, Lorenzo Stoakes wrote:
> ...
> > > I recall correctly that initially, merging vma-s with different
> > > VM_SORTDIRTY bit values was not allowed. It was a bit surprising that
> > > this behavior was changed by Cyrill in 34228d473efe.  Cyrill was an
> > > active CRIU contributor at the time, so we can't even blame anyone for
> > > breaking CRIU :).
> >
> > Well I think Cyrill is in the right here :) the problem described there -
> > that of hitting the max_map_count simply due to failed VM_SOFTDIRTY merges
> > - is very serious and clearly highlights the issue that arises from not
> > merging these - that is VMA fragmentation.
>
> Hi guys! Happen to miss this thread due to high message traffic, thanks
> for CC'ing me ;) Yeah, disability to merge VMAs due to softdirty bit has
> been a serious issue, so better criu to dump more (redundant) memory
> than apps got broken. As to this patch series, I think it is good, thanks
> a huge Lorenzo!
>
> Acked-by: Cyrill Gorcunov <gorcunov@...il.com>

Thanks :)