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[80.230.85.71]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-30ee2f5e4dcsm857053eec.5.2026.06.29.13.44.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 29 Jun 2026 13:44:20 -0700 (PDT) Date: Mon, 29 Jun 2026 16:43:56 -0400 From: "Michael S. Tsirkin" To: "David Hildenbrand (Arm)" Cc: Andi Kleen , linux-kernel@vger.kernel.org, Miaohe Lin , Naoya Horiguchi , Andrew Morton , Oscar Salvador , 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: <20260629164258-mutt-send-email-mst@kernel.org> References: <20260629033608-mutt-send-email-mst@kernel.org> <20260629043417-mutt-send-email-mst@kernel.org> <20a5dfd4-b3c7-450a-8a70-08d0345aade4@kernel.org> MIME-Version: 1.0 In-Reply-To: <20a5dfd4-b3c7-450a-8a70-08d0345aade4@kernel.org> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: uuNq9p4JvYGhbmAjsCJ1T6YySiMre_wr-9IIML5cFt8_1782765862 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: B0A6E100009 X-Rspam-User: X-Stat-Signature: gie43yekxehg1sop34rcssfm4zxdd4s3 X-HE-Tag: 1782765864-26205 X-HE-Meta: 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 lfCqlvhm wlXA97ClQP6+/LxLmjhgtnQq6I1IGrq8NUM3TNRTQ7uLBsrYG2OHVD7/SdN7LVXUXO2G4sRj/CvJrn2i/aZVAX0g+gy9g+oMmyFhET1K4XCBuEx9TdcXdAS/VssTdBSEg0TFDh3xXBH5qVtx6rUaKC1lhwsUyx2MeQI+PhS3cBQ4EmJeX6d4ndh74oEC+AjjmAjOAIbdyBJQr2Z0MHqC0NnmLuVwGgURd6Y2zhK5rKVybzFLxlRujmv4GnsfzUZoikn8kqiHdRjJK2USw4HwS6iLV5pZlnMWLDOv5doXPz/fmuRM8wq4/TAmx154yO0FkUuGxpA2tiqKQV6XmM9x0IbznROahxub/6+LFX1+BHAq1jwWunuzJ8qLEUIbGjIM/VQnoe6uuEdwR3Wk8wBkAwrZkpYKdS1KWlW3n Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Jun 29, 2026 at 07:04:25PM +0200, David Hildenbrand (Arm) wrote: > On 6/29/26 18:54, Andi Kleen wrote: > >> However, this was a basic test, when allocating 4k pages. With 2M hugepages: > >> > >> insns/iter cycles/iter > >> ------------------------------------------------------- > >> base 20758 +/- 12.5 191208 +/-1946.6 > >> rcu 20785 +/- 3.7 197108 +/- 132.1 > >> atomic 20727 +/- 6.4 204591 +/- 160.2 > >> > >> rcu vs base +27 (+0.13%) +5900 (+3.09%) > >> atomic vs base -31 (-0.15%) +13383 (+7.00%) > >> > >> and even with THP: > >> > >> insns/iter cycles/iter > >> ------------------------------------------------------- > >> base 27220 +/- 2.8 192151 +/- 483.3 > >> rcu 27248 +/- 30.1 194159 +/-2746.6 > >> atomic 27186 +/- 3.2 200526 +/- 746.2 > >> > >> rcu vs base +28 (+0.10%) +2008 (+1.04%) > >> atomic vs base -34 (-0.12%) +8374 (+4.36%) > >> > >> > >> needs more thought. > > > > Well the alternative is to not bother with RCU, but just wait a bit and > > check if the bit stuck and repeat if needed. While that could in theory > > livelock it is extremely unlikely (especially if you add a bit of randomization > > to the sleep) > > We discussed that a bit already. Hypervisors make it fairly unpredictable how > long you would actually have to spin. Way I see it, this is not the issue. The issue is it does not fix the race: CPU1: read flags CPU2: test and set test and set #2 - sees it is set CPU1: write flags clearing the bit > -- > Cheers, > > David