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AJvYcCV5aKGVWadvA+AhiNAUJWGiayFgic0JgIwbwiu+NVRQSG1KETzHDyN9H0GZJXcoQ+c09x6GVIXVcQ==@kvack.org X-Gm-Message-State: AOJu0YyXGJihNezNCFrqqXhSqMxSEvgvz/UStaLLrPjZ9yNrVB06Suit 970SLGH+y+PWVZrnuXGQ6HbNXidnjUa6+aBJoMYZ2p8lwcURa3HfwdN/54j0Ek+Paskfz5cV9cK sbj92UuYgY90XtEM0c7xmKyr2+5JDKfk= X-Gm-Gg: ASbGnctl8FB5N7FgmH4SPm0FM6VsdWfTH93sBCV8DfV+vPon0K1Y/vicrZJRr33SOrv 279FEAVnl7vcZKUuvvVp/OR9tYg/i2sJPKlJEQlUWfTWyjCV9iUgoU+8/nTeyU8J0zNw6TcGpe0 oRdtIokFRQT05aRZqJ3SZe1oLCVrTQlHp/gPEGeFDvNbRHTuLh9We87zxmPrAKAdD2ob7pBwdSe /rpM0prqdc3aAs52XZGCL1gTOrghQ6/0uALjqDb0MUe/FTta/t+l0K1jo/Bzw== X-Google-Smtp-Source: AGHT+IFF61CUQlCQyuFHaJQCHfCMYrdPrh0r5dTlUOQtn7WQOt1YdjTPj9U5FmvA/UbUQBPmyGv7Ji5FWFKgePiGy0E= X-Received: by 2002:a05:6870:e9a:b0:3c9:895a:d9ec with SMTP id 586e51a60fabf-3e868f17bd8mr5239920fac.17.1763404006346; Mon, 17 Nov 2025 10:26:46 -0800 (PST) MIME-Version: 1.0 References: <1c20ec44-0775-47e0-aabb-e1cf1f38ce94@lucifer.local> In-Reply-To: <1c20ec44-0775-47e0-aabb-e1cf1f38ce94@lucifer.local> From: Andrei Vagin Date: Mon, 17 Nov 2025 10:26:34 -0800 X-Gm-Features: AWmQ_bk15XTDnUj2arkWOdO7K-a4XlaHRTnUWQ9fD4al7Mgd8GhoD1S1ts7TM_A Message-ID: Subject: Re: [PATCH 0/2] make VM_SOFTDIRTY a sticky VMA flag To: Lorenzo Stoakes Cc: Andrew Morton , David Hildenbrand , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jann Horn , Pedro Falcato , linux-mm@kvack.org, linux-kernel@vger.kernel.org, criu@lists.linux.dev, Cyrill Gorcunov Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam12 X-Rspam-User: X-Rspamd-Queue-Id: 848F4140011 X-Stat-Signature: 6tct78ca5wikbt9ixtwpxbehbwj4hrkz X-HE-Tag: 1763404007-196587 X-HE-Meta: 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 1NGOTMgW NB8Q19zjGJHbE0IEEPPttTHjArw8hlybzfRK4M6gFatC3c0c1wcH3hZPcHmJ1P2O1gdXBeSsKGGG6xC2Kl9RT+yOIwxJY5NAKXOND7LETlXzCKStQymnSYIqLDpretx6A19JMt6ytwv8Vgi4iIa7BSHjfElRJTFVE3/bZfQc1Ibt8ewy3U8BVfebtSTEvwU1r62GTWUgjFWtKsuU7txrI95LPcSKPs8O1dZbG5h1UEbocqkHpyPiA1Wv5dljFFerZqVcKXPLUq+Vcwzjh2aGNV4O6x6G+5GriCz8CaR0kCvO6pNjl3a6geFpH0t38oJ1aoQ9OZy8GOQub28ls+L4TTGa2bJbHyCgpkolbE+SD9RWDQAm/8ctAjndCWg5/3YhWPP746K4AsSGCRE00Ql7ziDszKq0eteZF2Pax3LrYkRJOvGg= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Nov 17, 2025 at 3:33=E2=80=AFAM Lorenzo Stoakes wrote: > > On Sun, Nov 16, 2025 at 04:53:36PM -0800, Andrei Vagin wrote: > > On Fri, Nov 14, 2025 at 9:59=E2=80=AFAM Lorenzo Stoakes > > wrote: > > > > > > Currently we set VM_SOFTDIRTY when a new mapping is set up (whether b= y > > > establishing a new VMA, or via merge) as implemented in __mmap_comple= te() > > > and do_brk_flags(). > > > > > > However, when performing a merge of existing mappings such as when > > > performing mprotect(), we may lose the VM_SOFTDIRTY flag. > > > > Losing VM_SOFTDIRTY is definitely a bug, thank you for fixing it. > > > > A separate concern is whether merging two VMAs should be permitted when > > one has the VM_SOFTDIRTY flag set and another does not. I think the > > merging operation should be disallowed.The issue is that > > > This patch doesn't change anything in terms of merging, it only _correctl= y_ > marks VMAs as soft-dirty where certain, very specific, circumstances migh= t > result in a merged VMA being incorrectly indicated to not be soft-dirty > when it in fact contains pages which are. As I mentioned in the previous message, this patch is correct, and I appreciate your effort to solve this issue. My comment was about whether we should allow merging VMAs if one has VM_SOFTDIRTY and the other does not. You are right, this is a separate question unrelated to this patch. 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 :). Thanks, Andrei