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Mon, 02 Nov 2026 07:04:35 +0000 X-Mizu-Trace-ID: 4b82456d18ca3934 X-Migadu-Flow: FLOW_OUT From: Lance Yang To: david@kernel.org Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, mhocko@kernel.org, qi.zheng@linux.dev, shakeel.butt@linux.dev, ljs@kernel.org, kasong@tencent.com, baohua@kernel.org, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, baoquan.he@linux.dev, baolin.wang@linux.alibaba.com, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, kees@kernel.org, peterz@infradead.org, jannh@google.com, pfalcato@suse.de, hughd@google.com, pasha.tatashin@soleen.com, pratyush@kernel.org, willy@infradead.org, jack@suse.cz, ziy@nvidia.com, lance.yang@linux.dev, riel@surriel.com, harry@kernel.org, apopple@nvidia.com, nico.pache@linux.dev, ryan.roberts@arm.com, dev.jain@arm.com, usama.arif@linux.dev, kas@kernel.org, matthew.brost@intel.com, jhubbard@nvidia.com, peterx@redhat.com, will@kernel.org, aneesh.kumar@kernel.org, npiggin@gmail.com, osalvador@suse.de, minchan@kernel.org, muchun.song@linux.dev, xu.xin@linux.dev, chengming.zhou@linux.dev, chrisl@kernel.org, shikemeng@huaweicloud.com, nphamcs@gmail.com, youngjun.park@lge.com, gourry@gourry.net, joshua.hahnjy@gmail.com, rakie.kim@sk.com, ying.huang@linux.alibaba.com, jgg@ziepe.ca, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-cxl@vger.kernel.org, usama.anjum@arm.com Subject: Re: [PATCH v3 18/47] mm/khugepaged: check if PTE table is empty in try_collapse_pte_mapped_thp() Date: Mon, 2 Nov 2026 15:04:26 +0800 Message-ID: <20261102070426.45406-1-lance.yang@linux.dev> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20261031-fixes_core-v3-18-d6437171ecc3@kernel.org> References: <20261031-fixes_core-v3-18-d6437171ecc3@kernel.org> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 63F5D1A0006 X-Stat-Signature: kk5xk1f1uhmkcbm5781aoqo4kikxppog X-Rspam-User: X-Spam-Status: No, score=-13.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS, USER_AGENT_GIT autolearn=ham autolearn_force=no version=4.0.1 X-HE-Tag: 1793603078-512324 X-HE-Meta: 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 r9iLLvSg 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 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 Sat, Oct 31, 2026 at 10:39:47AM +0100, David Hildenbrand (Arm) wrote: >The existing code is rather horrible and already resulted in bugs in the >past: we special-case UFFD inserting anonymous folios by grabbing the PMD >lock early, but ignore any other markers (guard, poison through uffd) that >could have been inserted into the page table in the meantime, effectively >dropping them. > >Let's just unify and simplify the locking: try to grab the PMD table >lock and if that fails, flush the TLB, drop the PTE lock, take PT locks in >the right order and check if the page table is still empty. Yep ;) Taking the PMD lock up front would make the locking easier to follow, though we'd hold it across all the PTE zapping ;) >We still perform the heavy lifting (zapping the folio ptes) under PTE table >lock only. > >Include for now, as x86's flush_tlb_range() macro >depends on hugetlb helpers. This dependency needs a separate cleanup. > >Both issues this fixes are rather corner cases. Let's not CC stable for >now. > >Fixes: f807123d578d ("mm: allow guard regions in file-backed and read-only mappings") >Fixes: 1043173eb5eb ("mm/khugepaged: collapse_pte_mapped_thp() with mmap_read_lock()") >Tested-by: Gregory Price (Meta) >Reviewed-by: Gregory Price (Meta) >Tested-by: Muhammad Usama Anjum >Signed-off-by: David Hildenbrand (Arm) >--- LGTM! Reviewed-by: Lance Yang