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Wed, 22 Jul 2026 02:58:15 -0700 (PDT) Message-ID: <2e9902e7-3f40-49d5-afb0-e710fb01ab39@gmail.com> Date: Wed, 22 Jul 2026 17:58:00 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 4/4] mm/mlock: migrate folios out of CMA when mlocking a range To: Sebastian Andrzej Siewior , "David Hildenbrand (Arm)" Cc: vbabka@kernel.org, rostedt@goodmis.org, mhiramat@kernel.org, Alexander.Krabler@kuka.com, hughd@google.com, fvdl@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev, akpm@linux-foundation.org, surenb@google.com, mhocko@suse.com, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, ljs@kernel.org, riel@surriel.com, liam@infradead.org, harry@kernel.org, jannh@google.com, lance.yang@linux.dev, mathieu.desnoyers@efficios.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, apopple@nvidia.com, pfalcato@suse.de References: <20260707125925.3725177-1-chenwandun1@gmail.com> <20260707125925.3725177-5-chenwandun1@gmail.com> <9b227263-56d9-41d5-ba8e-c969d8d68785@kernel.org> <20260709131509.iIPP2VBh@linutronix.de> Content-Language: en-US From: Wandun In-Reply-To: <20260709131509.iIPP2VBh@linutronix.de> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: B72D7180007 X-Stat-Signature: uhmi3m3d36kqtd7ifagmcy7rori4ip5j X-HE-Tag: 1784714297-370973 X-HE-Meta: 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 94fNUM87 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Sebastian, David, Sorry for the long delay in getting back to this, and thanks a lot for the review. On 7/9/26 21:15, Sebastian Andrzej Siewior wrote: > On 2026-07-09 12:04:33 [+0200], David Hildenbrand (Arm) wrote: >> On 7/7/26 14:59, Wandun Chen wrote: >>> From: Wandun Chen >>> >>> The region covered by mlock[all] may contain CMA pages. cma_alloc installs >> >> What about ZONE_MOVABLE where memory is supposed to be migratable? > > Would it be bad if the pages would not be movable anymore? Does this > effect just memory-hotplug or something else, too? ZONE_MOVABLE does not need the same treatment as CMA. 1. On RT compact_unevictable_allowed is 0 by default, pages in ZONE_MOVABLE are never migrated by compaction, so no latency spike, no problem. 2. For the scenario of memory offlining within ZONE_MOVABLE, because of offline is an explicit administrator action. Any jitter/latency is expected and acceptable, the operator chose to offline memory and would not do so during an RT-critical phase. 3. cma_alloc() runs at runtime, triggered by drivers as part of normal operation, and isolation path hardcodes ISOLATE_UNEVICTABLE, so it migrates the mlocked pages and installs migration entries. The fault-and-wait latency hits the RT task unpredictably during normal operation, which is not expected, and is exactly the spike this patch targets. > >> Also, what about drivers that mmap() CMA memory to user space, and >> __mm_populate()->populate_vma_page_range() would actually try mlocking them, and >> they actually must remain on CMA areas? > > It should be safe to skip those. They belong to device and they > shouldn't be affected by anything including getting swapped out. Agreed. Only LRU folios are ever isolated for migration here (isolate_folio_to_list() -> folio_isolate_lru()), and device-owned CMA buffers are not on the LRU, so they are left in place. I'll double-check the mmap paths and make sure this holds, and state it explicitly in v3. Best regards, Wandun > > Sebastian