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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> 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 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.