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[80.230.85.71]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-475641e4618sm2067879f8f.9.2026.06.29.16.34.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 29 Jun 2026 16:34:43 -0700 (PDT) Date: Mon, 29 Jun 2026 19:34:38 -0400 From: "Michael S. Tsirkin" To: "David Hildenbrand (Arm)" Cc: linux-kernel@vger.kernel.org, Miaohe Lin , Naoya Horiguchi , Andrew Morton , Oscar Salvador , Andi Kleen , Hidehiro Kawai , Rik van Riel , Vlastimil Babka , Lorenzo Stoakes , "Liam R. Howlett" , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Christoph Lameter , David Rientjes , Roman Gushchin , Harry Yoo , Hao Li , Kiryl Shutsemau , Byungchul Park , linux-mm@kvack.org, linux-cxl@vger.kernel.org Subject: Re: [PATCH 0/2] mm: memory-failure: fix HWPoison flag race with non-atomic page flag ops Message-ID: <20260629193347-mutt-send-email-mst@kernel.org> References: <0b5f8b4b-d7dc-4b79-9555-a5b36265f3a9@kernel.org> <20260629030657-mutt-send-email-mst@kernel.org> <4f5ba5d6-246c-4430-9737-e8dd8e4c5142@kernel.org> <20260629092856-mutt-send-email-mst@kernel.org> <54c8cbee-9b26-458c-93ba-5aa594f5d1e8@kernel.org> <0a309ed3-378e-4d88-95a0-65bf47c5496d@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0a309ed3-378e-4d88-95a0-65bf47c5496d@kernel.org> On Mon, Jun 29, 2026 at 11:43:32PM +0200, David Hildenbrand (Arm) wrote: > On 6/29/26 23:22, David Hildenbrand (Arm) wrote: > > [...] > > > >> > >> And again, I'm really not sure fixing a theoretical race when memory > >> is failing is worth slowing the world by 0.1-1% for. > >> > > > > Fully agreed. I was hoping RCU was cheaper (I mean, we were once told that RCU > > read side locking is essentially for free ... well in some configs :) ) > > > > The question if we could optimize it reasonably enough ... > > > >> > >> From what I saw in my testing, if we allocate 4k pages > >> it's hidden by the overhead. With hp and thp it's measureably > >> worse than rcu on !preempt config. > > > > ... for example, by doing the rcu read lock + unlock around the > > > > for (i = 1; i < (1 << order); i++) { > > > > loop on the alloc path. But I suspect it's not going to make that much of a > > difference. > > > > I concluded, similar to Andi, that stop_machine() is too big of a hammer. > > > > I wonder if something could be built out of preempt_disable() and sync SMP > > calls. hmm :( > > Scrap that, shouldn't work I think ... > Wait a sec, what about call_rcu_tasks? Use that and re-check the bit is still set? -- MST