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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id 46e09a7af769-718615068f1sm1001454a34.8.2024.10.26.22.08.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 26 Oct 2024 22:08:25 -0700 (PDT) Date: Sat, 26 Oct 2024 22:08:13 -0700 (PDT) From: Hugh Dickins To: Yang Shi cc: Zi Yan , Hugh Dickins , Andrew Morton , Usama Arif , Wei Yang , "Kirill A. Shutemov" , Matthew Wilcox , David Hildenbrand , Johannes Weiner , Baolin Wang , Barry Song , Kefeng Wang , Ryan Roberts , Nhat Pham , Chris Li , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH hotfix 1/2] mm/thp: fix deferred split queue not partially_mapped In-Reply-To: Message-ID: <5d28df34-f073-dec5-730e-a3073f14d849@google.com> References: <760237a3-69d6-9197-432d-0306d52c048a@google.com> <3A1E5353-D8C5-4D38-A3FF-BFC671FC25CE@nvidia.com> <966a4aff-f587-c4bb-1e10-2673734c2aa0@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspamd-Queue-Id: 34BD2180008 X-Stat-Signature: qh38r3i4sgygqz7hgu4bfbp8xu1m64cy X-Rspamd-Server: rspam09 X-Rspam-User: X-HE-Tag: 1730005704-594547 X-HE-Meta: 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 /rcTpIlM UYAq5Z1y301yoOipLyAjfbpdKvDXUSRcIt2d3ho/5WgRxn2F/hLdF6XJcXpr8uRPkMtKwuKzLp5YdF3f8O11cKto3xIS5PKvdtcGuHrwAtTlxyLdh6z5Peu8S9TqNIBagzIst+6c1OYWK/wG0h6o9LBnY4vNV7oVCWQPuyNC7L5xf9dDWsqb7ir9F2Asurwccin2h4dVA3f98NLo2aHCKYatr0fzGoI2IHKHTneX826RQSWcWyCSC8N/yiVN6fv9NKQ23+0p3lQNaKu/Hr6+584Awlt0SVwweIiHezkIVPYBVbojgWX8E6jrJgS6RbbfqU+KQD5l+mqxIZWRbyB/ZAsbPWxXNrpLQJq3P57TDAFGFk6Zcfcwl8C0+kLwCYYLcKeHsNMz5YbD0Eh4kpE/mad6An36IiqkS/wK7gBbM7zleC5x6ZGgttwMZPyqv0r17mrG7oXjlMlvLGBOccE7jFNtPFrSYiQwGZkGe 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 Fri, 25 Oct 2024, Yang Shi wrote: > > The other subtle thing is folio->_deferred_list is reused when the > folio is moved to the local on-stack list. And some Yes. > list_empty(deferred_list) checks return true even though the folio is > actually on the local on-stack list. Some code may depend on or The code definitely depends on that behaviour: that's how folios get unqueued when refcount reaches 0, whether they are on the public list or on the local list at that time. > inadvertently depend on this behavior. Using folio_batch may break > some assumptions, but depending on this subtle behavior is definitely > not reliable IMHO.