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

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Message-ID: <aR3BndGWuzf8vnku@grain>
Date: Wed, 19 Nov 2025 16:09:49 +0300
From: Cyrill Gorcunov <gorcunov@...il.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.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 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>