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Thu, 09 Jul 2026 01:25:42 -0700 (PDT) Message-ID: Date: Thu, 9 Jul 2026 16:25:27 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/4] mm/migrate: do not migrate folios mapped into VM_LOCKED VMAs under compaction To: Lorenzo Stoakes Cc: vbabka@kernel.org, david@kernel.org, rostedt@goodmis.org, mhiramat@kernel.org, Alexander.Krabler@kuka.com, hughd@google.com, fvdl@google.com, bigeasy@linutronix.de, 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, 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> <20260707125925.3725177-2-chenwandun1@gmail.com> Content-Language: en-US From: Wandun In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: e8kcy8uiigpe6cqmkpueohbh17cwox1x X-Rspamd-Queue-Id: 6A4E1180003 X-Rspamd-Server: rspam01 X-Rspam-User: X-HE-Tag: 1783585545-744037 X-HE-Meta: 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 iZz5vQRl 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/7/26 21:55, Lorenzo Stoakes wrote: > On Tue, Jul 07, 2026 at 02:44:50PM +0100, Lorenzo Stoakes wrote: >> See above about deduplicating. >> >>> + ttu |= TTU_RESPECT_MLOCK; >> >> Hmm. I don't love 'respect mlock'. I guess we only know about the reason >> being compaction here. >> >> But I'm confused anyway. We have the folio, why aren't we just checking for >> PG_mlocked() here instead of getting the rmap to see if it's mapped >> anywhere with VMA_LOCKED_BIT? > > Also, since compaction_allow_unevictable() is a function that is accessible > elsewhere, you could literally just have a TTU_MIGRATION here instead and have > the rmap logic call compaction_allow_unevictable() instead rather than this. Do you mean: 1. change TTU_RESPECT_MLOCK to TTU_MIGRATION, that'is OK. 2. move call compaction_allow_unevictable() to try_to_migrate_one? but as you suggested migrate_mlock_allowed function, it already called compaction_allow_unevictable() in order to determine whether TTU_MIGRATION needs to be added. Did I misunderstand something somewhere? > > And then you could adapt the function I suggested before not to take a reason > parameter but rather a 'is_migration' one instead possibly and then pass (ttu & > TTU_MIGRATION) in. > > BUT. I still question whether this is at all needed since you have the folio you > can check for PG_mlocked... I described a race scenario at this link: https://lore.kernel.org/lkml/c372e68f-2bfc-45b6-a431-01bf55717247@gmail.com/ > > Cheers, Lorenzo