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Mon, 9 Jun 2025 09:06:04 -0700 (PDT) Date: Mon, 9 Jun 2025 09:06:04 -0700 (PDT) From: "Christoph Lameter (Ampere)" To: Harry Yoo cc: vbabka@suse.cz, rientjes@google.com, akpm@linux-foundation.org, roman.gushchin@linux.dev, willy@infradead.org, linux-mm@kvack.org Subject: Re: [PATCH] mm/slab: fix folio_test_{anon,ksm}() false positive on slabs In-Reply-To: <20250609132723.13118-1-harry.yoo@oracle.com> Message-ID: <3fcbe4a8-dfc6-c708-f765-859d9f191c91@gentwo.org> References: <20250609132723.13118-1-harry.yoo@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 0549940002 X-Stat-Signature: s9medjfw1ergqedgb1komrq4hjcpew5t X-Rspam-User: X-HE-Tag: 1749485165-598575 X-HE-Meta: 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 8b9+Wl7k kHUh3zZgnwbUo74h7OQm88Q+C1itHuysnkFC0YW3VIGYN5C2Bm8xBR4sU3ZVBHtcwOTEWk9mcZk38FUfBTghLxOXGM7mJX142fb+ssYsi7XNwgUsQnU8bcqQcbf9PBLegThM9lHuQ7OMbQl5pYBuw4tXImj9M2TTi/RdfoGB0UOHMbBS9P1mWg/tPLVvnr3VSZ7ZAkEr0uoYE1VJI8NJQKbKszCh7Y9VXVvmhslzLitdy6wnqUuDra4c7dxSmVvoSiSq2yw2RkomcXeLonia394C6F25WiAVPHFimeBZRs3DdO6c= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000003, 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, 9 Jun 2025, Harry Yoo wrote: > [ field ] [ offset ] [ size ] > page->mapping 24 8 > page->lru 8 16 > > slab->next 16 8 > slab->slabs 24 4 > > Reorder ->slabs and ->next, so that the layout will be: > > slab->slabs 16 4 > slab->next 24 8 > > After reordering, slab->slabs shares its offset with page->lru.prev, > which is not a problem. slab->next now shares the offset with > page->mapping, but that's fine, as a slab is double-word aligned. Add comments to document the trickery that is going on here? Otherwise we may stumble across this issue again later.