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Fri, 06 Nov 2026 01:29:53 -0800 (PST) Received: from localhost.localdomain ([240e:b8f:1df9:a600:c693:b19f:ada0:748]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3b0b326add7sm7043845a91.8.2026.11.06.01.29.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 06 Nov 2026 01:29:52 -0800 (PST) Date: Fri, 6 Nov 2026 17:29:45 +0800 From: Vernon Yang To: "Lorenzo Stoakes (ARM)" Cc: David Hildenbrand , Zi Yan , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kiryl Shutsemau , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 3/3] mm/khugepaged: release contended mmap read lock after scanning enough VMAs Message-ID: References: <20261105-khugepaged-latency-fix-v2-0-4384bbfe4606@kernel.org> <20261105-khugepaged-latency-fix-v2-3-4384bbfe4606@kernel.org> <257ab860-b408-4897-838b-e7b68f981d6c@gmail.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <257ab860-b408-4897-838b-e7b68f981d6c@gmail.com> On Fri, Nov 06, 2026 at 10:12:46AM +0800, Vernon Yang wrote: > On Thu, Nov 05, 2026 at 08:57:24PM +0000, Lorenzo Stoakes (ARM) wrote: > > if (!collapse_possible_orders(vma, vma->vm_flags, TVA_KHUGEPAGED)) { > > - /* Unable to collapse, skip to the next candidate. */ > > - mm_slot->address = ALIGN(vma->vm_end, HPAGE_PMD_SIZE); > > + const unsigned long next = > > + ALIGN(vma->vm_end, HPAGE_PMD_SIZE); > > + > > cc->progress++; > > + /* Check for overflow. */ > > + if (unlikely(next < vma->vm_end)) { > > I think you want it to be like that. > > if (unlikely(next >= vma->vm_end)) { > ^^ Don’t read this comment please. Your code is right. The VMA at the top of mm, after aligning the end values according to the PMD, may overflow to 0. It might be easier to understand if this coding is used. if (unlikely(next == 0)) { -- Cheers, Vernon