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Mon, 13 Jul 2026 18:45:15 -0700 (PDT) Message-ID: <97c1dccb-8f17-45f3-8058-023da96620c8@gmail.com> Date: Tue, 14 Jul 2026 09:45:01 +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-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 59E23160003 X-Stat-Signature: 8aunxqd4ewe6d6znbn5bqceh3hom1i16 X-HE-Tag: 1783993517-127966 X-HE-Meta: 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 O6/vd2tc 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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 7/9/26 23:00, Lorenzo Stoakes wrote: > On Thu, Jul 09, 2026 at 04:25:27PM +0800, Wandun wrote: >> >> >> 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? > > The next paragraph addresses this. > >> >>> >>> 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/ > > OK thanks. You really have to spell this out in the code in a comment, this is > really non-obvious. I will address these in the next version. Thanks, Wandun > > I will try to look at your reply in due course (am between jobs atm). > >> >> >>> >>> Cheers, Lorenzo >> > > Thanks, Lorenzo