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Fri, 30 Oct 2026 03:24:34 +0000 X-Mizu-Trace-ID: 13ff5ce3ac3bfaeb X-Migadu-Flow: FLOW_OUT From: xu.xin@linux.dev To: david@kernel.org Cc: akpm@linux-foundation.org, aneesh.kumar@kernel.org, apopple@nvidia.com, axelrasmussen@google.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, baoquan.he@linux.dev, chengming.zhou@linux.dev, chrisl@kernel.org, dev.jain@arm.com, gourry@gourry.net, hannes@cmpxchg.org, harry@kernel.org, hughd@google.com, jack@suse.cz, jannh@google.com, jgg@ziepe.ca, jhubbard@nvidia.com, josef@toxicpanda.com, joshua.hahnjy@gmail.com, kas@kernel.org, kasong@tencent.com, kees@kernel.org, kexec@lists.infradead.org, lance.yang@linux.dev, liam@infradead.org, linux-arch@vger.kernel.org, linux-cxl@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, ljs@kernel.org, matthew.brost@intel.com, mhocko@kernel.org, mhocko@suse.com, minchan@kernel.org, muchun.song@linux.dev, nico.pache@linux.dev, nphamcs@gmail.com, npiggin@gmail.com, osalvador@suse.de, pasha.tatashin@soleen.com, peterx@redhat.com, peterz@infradead.org, pfalcato@suse.de, pratyush@kernel.org, qi.zheng@linux.dev, rakie.kim@sk.com, riel@surriel.com, rppt@kernel.org, ryan.roberts@arm.com, shakeel.butt@linux.dev, shikemeng@huaweicloud.com, stable@vger.kernel.org, surenb@google.com, usama.arif@linux.dev, vbabka@kernel.org, weixugc@google.com, will@kernel.org, willy@infradead.org, xu.xin@linux.dev, ying.huang@linux.alibaba.com, youngjun.park@lge.com, yuanchu@google.com, ziy@nvidia.com Subject: [PATCH 38/46] mm/ksm: reset the unstable trees of all nodes Date: Fri, 30 Oct 2026 11:24:09 +0800 Message-Id: <20261030032409.127393-1-xu.xin@linux.dev> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20261027-fixes_core-v1-38-6f74bec9a5bb@kernel.org> References: <20261027-fixes_core-v1-38-6f74bec9a5bb@kernel.org> X-Archived-By: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 2B12F180002 X-Stat-Signature: 9aahwrq6g8e3yxhwu7s4ate8xpr7woig X-Rspam-User: X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=4.0.1 X-HE-Tag: 1793330675-776194 X-HE-Meta: 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 j0stDc8v XAelvl9U0Mc4afE9cf9eZ1pSCL7eysDM4X/gRDzQsV1Jq2+nltBm2ra9XEkIeSNekOo22bkf3SE5XRrfqTcnd4K3kH60EUgyPFmbbGiSP1VMJorEAsPjTg+tW26OoV2k+oNo27p+QF3vQbBRVFvExNn4ijRoalABVeebTz8tJg2H1wuTubbwSgtBGuKzrYdtjFMNqXvAbrheCVzJToLn5hL6FHmGeySeSgQ/iKp8VlUtwQGa/0ZFd+fx+78wda+uR7ytxYCFrL7LtjtPLSdLxghF9t8qfZfLlk3u3dV8rDr6Y17yWX+Y4u6cPSRUBbb8AtxG11pBUNK6/t3M3KfBahAYu7M5YA7ZaNw5jrPktRLHwvWv2q1oZgD+nLvvjlR+uRxmw 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 > > Let's fix it by tracking in ksm_nr_node_ids the actual number of > allocated tree roots. > > remove_all_stable_nodes() and ksm_check_stable_tree() will now scan > more tree roots (skipping the empty ones), which is harmless. > > Fixes: ef53d16cded7 ("ksm: allocate roots when needed") > Cc: stable@vger.kernel.org > Reported-by: Josef Bacik > Signed-off-by: David Hildenbrand (Arm) > --- > mm/ksm.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/mm/ksm.c b/mm/ksm.c > index dbfb8f98b1892..9c51925825cbf 100644 > --- a/mm/ksm.c > +++ b/mm/ksm.c > @@ -475,6 +475,7 @@ static void advisor_stop_scan(void) > #ifdef CONFIG_NUMA > /* Zeroed when merging across nodes is not allowed */ > static unsigned int ksm_merge_across_nodes = 1; > +/* Number of allocated stable and unstable tree roots. */ > static int ksm_nr_node_ids = 1; > #else > #define ksm_merge_across_nodes 1U > @@ -3636,14 +3637,13 @@ static ssize_t merge_across_nodes_store(struct kobject *kobj, > else { > root_stable_tree = buf; > root_unstable_tree = buf + nr_node_ids; > + ksm_nr_node_ids = nr_node_ids; > /* Stable tree is empty but not the unstable */ > root_unstable_tree[0] = one_unstable_tree[0]; > } > } > - if (!err) { > + if (!err) > ksm_merge_across_nodes = knob; > - ksm_nr_node_ids = knob ? 1 : nr_node_ids; > - } > } > mutex_unlock(&ksm_thread_mutex); > > > -- > 2.43.0 Looks correct as far as it goes, but I think it is not quite sufficient on its own. The documentation requires that merge_across_nodes can only be changed when there are no KSM shared pages in the system, but merge_across_nodes_store() does not enforce this at the sysfs level. Should we also reject writes while ksmd is merging? At minimum: + if (ksm_run & KSM_RUN_MERGE) + return -EBUSY; Ideally, we should also check that ksm_pages_shared is zero, since KSM_RUN_STOP (0) does not guarantee that all pages have been unmerged. That would make the interface match the documented sequence and close the remaining race window.