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a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=9xMycIWfnUiEotnezQAVhJSgjXTaz5NeZUJ91/GQmTM=; b=FunM1A/FNHEQQ4Ld5+6LQqOynPgVndkQLczW4VYGewBWC6n66YAsxBoIe44m6LR+Dx pflySJ5YT4/gblwgxQZYHpdzl+OOcGt8He8bqCmWOEer6yeUXaIu7ZVfiKOkFarXTXaI pUfQqD5ggMsUFDls9UNCorzQ8Cse7/a/j0NhhIPc+fZz/QizyFW82LmfsRydxWXpzhJB re9duvjKmaZPN5gZlGYxyI2QONjlHJSNAUtK1ktD4tGoXGMRT30Oq1DdN7IbMN6i7z1s 359a+7NIfUJltMtma58OP8Tp3tRW+7xOAcdy8M7ekZg83/Cf6g82hnoHgffYpmJZApBL 5ucw== X-Gm-Message-State: AO0yUKXt86ds/6mNh8vyB/Tpzu1x7BowfgFiis76HahrFkjQuXXC+lrY EFpjcJam9MM9pKCQmzDLCvCePnDcI7QLui6N8xY1uQ== X-Google-Smtp-Source: AK7set/VuWkYiW3ghjj83YQK/NAbeLBosLL9HfBpsEETKwrAvN0l7/CtP3vwkiphVG1dJGxO4zxlOEPhH2xE/Lcwl+s= X-Received: by 2002:a25:5209:0:b0:80b:5988:2045 with SMTP id g9-20020a255209000000b0080b59882045mr1119372ybb.59.1674754491393; Thu, 26 Jan 2023 09:34:51 -0800 (PST) MIME-Version: 1.0 References: <20230125233554.153109-1-surenb@google.com> <20230125233554.153109-7-surenb@google.com> <20230126154740.j3a3lu4x557c56yi@techsingularity.net> <20230126173245.cf3jcfw5s2a77s5v@techsingularity.net> In-Reply-To: <20230126173245.cf3jcfw5s2a77s5v@techsingularity.net> From: Suren Baghdasaryan Date: Thu, 26 Jan 2023 09:34:35 -0800 Message-ID: Subject: Re: [PATCH v3 6/7] mm: introduce mod_vm_flags_nolock and use it in untrack_pfn To: Mel Gorman Cc: akpm@linux-foundation.org, michel@lespinasse.org, jglisse@google.com, mhocko@suse.com, vbabka@suse.cz, hannes@cmpxchg.org, dave@stgolabs.net, willy@infradead.org, liam.howlett@oracle.com, peterz@infradead.org, ldufour@linux.ibm.com, paulmck@kernel.org, mingo@redhat.com, will@kernel.org, luto@kernel.org, songliubraving@fb.com, peterx@redhat.com, david@redhat.com, dhowells@redhat.com, hughd@google.com, bigeasy@linutronix.de, kent.overstreet@linux.dev, punit.agrawal@bytedance.com, lstoakes@gmail.com, peterjung1337@gmail.com, rientjes@google.com, axelrasmussen@google.com, joelaf@google.com, minchan@google.com, jannh@google.com, shakeelb@google.com, tatashin@google.com, edumazet@google.com, gthelen@google.com, gurua@google.com, arjunroy@google.com, soheil@google.com, hughlynch@google.com, leewalsh@google.com, posk@google.com, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, x86@kernel.org, linux-kernel@vger.kernel.org, kernel-team@android.com Content-Type: text/plain; charset="UTF-8" X-Stat-Signature: pb63y6mdk4n9dupcrzdo8e9amaoccuge X-Rspam-User: X-Rspamd-Queue-Id: A06DDC0010 X-Rspamd-Server: rspam06 X-HE-Tag: 1674754492-147812 X-HE-Meta: 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 CB9sKG5h VzU15HK08anNSKjrO8uahiqiDljcvTwT9oOY4tNOhp9umUhaeUy2buz2g4axyeFozZ49bDbuYJshgg2oCaEg+9oMh0XBo/e+civ4aePJqxRd33T/YWqKG4zhWfwHHUbIFPU2bk3q5we0uJnN2KBYy3R+ReCmUCQ6H8Dg02qKkIDaFXxg7j6Ni/4r0piI4qlyfIZ/4oJTMPcZHM4J6sl9k+zSGcbS4jOEcddd4kIYk0AWbe3oLTqH/Y5rjiptI3nbazhn+SV8QkP2Fp4sMYil12JfL4nhqkRSEjA3SO6wgd5TUgQ/lQbY/5zxOm9u+bl1YQx8hzQn40FPWlKKVS5YuWHvBijdsfoTvBvDiA3a9scjhqUo7s24uMwLQxA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Jan 26, 2023 at 9:32 AM Mel Gorman wrote: > > On Thu, Jan 26, 2023 at 08:18:31AM -0800, Suren Baghdasaryan wrote: > > On Thu, Jan 26, 2023 at 7:47 AM Mel Gorman wrote: > > > > > > On Wed, Jan 25, 2023 at 03:35:53PM -0800, Suren Baghdasaryan wrote: > > > > In cases when VMA flags are modified after VMA was isolated and mmap_lock > > > > was downgraded, flags modifications would result in an assertion because > > > > mmap write lock is not held. > > > > > > Add note that it's also used during exit when the locking of the VMAs > > > becomes irrelevant (mm users is 0, should be no VMA modifications taking > > > place other than zap). > > > > Ack. > > > > > > > > The typical naming pattern when a caller either knows it holds the necessary > > > lock or knows it does not matter is __mod_vm_flags() > > > > Ok. It sounds less explicit but plenty of examples, so I'm fine with > > such rename. Will apply in the next version. > > > > It might be a personal thing. nolock to me is ambigious because it might > mean "lock is already held", "no lock is necessary" or "no lock is acquired" > where as *for me*, calling foo vs __foo *usually* means "direct callers of > __foo take care of the locking, memory ordering, per-cpu pinning details etc" > depending on the context. Of course, this convention is not universally true. > > > > > Pass a hint to untrack_pfn to conditionally use mod_vm_flags_nolock for > > > > flags modification and to avoid assertion. > > > > > > > > Signed-off-by: Suren Baghdasaryan > > > > > > Patch itself looks ok. It strays close to being "conditional locking" > > > though which might attract some complaints. > > > > The description seems to accurately describe what's done here but I'm > > open to better suggestions. > > I don't have alternative suggestions but if someone else reads the patch and > says "this is conditional locking", you can at least claim that someone > else considered "conditional locking" and didn't think it was a major > problem in this specific patch. Perfect. Thanks! > > -- > Mel Gorman > SUSE Labs