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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-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=no autolearn_force=no version=4.0.1 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 8FF16C0003 X-Stat-Signature: 8hx95kydo66himmxp8upzb51t471pkkk X-Rspam-User: X-HE-Tag: 1793962177-408411 X-HE-Meta: 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 utR3ADWr 2ziiFxMIc/MNIeDst4JdgYEwpOUsX1iHZbrawvUUD41ijGD5H7PhWfXMs6gvn6Rbv4yGL8THGAX2cw3ypum2tG3f39umd+OT+h7YfdFc8+thAILshP/dD7fJwRwuP++8kLDXMxIKGTyUB4tyMNAj/nCI1q/rd7BC99VEgHm0jy5oKGsdGwikAtBuLDpHnmY3OUtRvqiTSzE1kHbRj/Xdy2A+fg51CVlpqJIRuGFC4uEJPQbH7pfQuEODuym7lFLAlqn5CsPM895BLHfWiuXdN548Cxw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Fri, Nov 06, 2026 at 05:29:45PM +0800, Vernon Yang wrote: > 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)) { I'd rather keep < as it's the general form used for overflow checks and I don't want to bake in assumptions about the nature of the overflow or make somebody have to reason about that :) > > -- > Cheers, > Vernon -- Cheers, Lorenzo