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[2003:cb:c710:8800:a73c:ec5b:c02c:5e0b]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4215c364bcdsm13086275e9.19.2024.06.06.01.33.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 06 Jun 2024 01:33:27 -0700 (PDT) Message-ID: Date: Thu, 6 Jun 2024 10:33:26 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v11 09/12] mm: implement LUF(Lazy Unmap Flush) defering tlb flush when folios get unmapped To: Byungchul Park , Dave Hansen Cc: Byungchul Park , linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel_team@skhynix.com, akpm@linux-foundation.org, ying.huang@intel.com, vernhao@tencent.com, mgorman@techsingularity.net, hughd@google.com, willy@infradead.org, peterz@infradead.org, luto@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, rjgolo@gmail.com References: <20240531092001.30428-1-byungchul@sk.com> <20240531092001.30428-10-byungchul@sk.com> <26dc4594-430b-483c-a26c-7e68bade74b0@redhat.com> <20240603093505.GA12549@system.software.com> <20240604015348.GB26609@system.software.com> <20240604044348.GA40889@system.software.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 0A74816000E X-Stat-Signature: huc8wryxs7emwafptky5hhqy98wza3nw X-Rspam-User: X-Rspamd-Server: rspam11 X-HE-Tag: 1717662811-101565 X-HE-Meta: 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 mq5vny/i +oZqG9lYhG/2ukpsxk65+iY4r9jEeEhPPO4/bsjUSVVb5AKoboSWCnL3q2ZLOZLTIzaIGYnQFdvF2ekZIXHue4usuDzqbFTPCN5rIdi7K9SIJwEh5Uzn5ouDoXd7WbW9tWnMKYjOQj/Sa8rrKNW8J5Sd83Q0G3plI6iwUDM55Rej2ZONJwQ17In3PYwjCh2yY4yRsC55GW35fB4Pal2lfeAzVbVMed0Qumkq+Pfob9FUvRtazs4nZSTvh42DqLI6q+rhcfqipPsLdEwNKubiT9IPbvuPhTAan89fjfW3D2jkg6bXmtj8qHt+/yuuO2zl66Yc4cjpScxHmd7Y8zk5xk+hfWRbPzexYIiv52BchGU47QoAg5HtIwy3Zj+cu0Jq2AzQAYDm2UA8nwboBTausFM1gnYDTPo5bXa4qCLW+GeMMyzUbiVdAbrSWjduS92JAxdCuHQTzvhxF2A+loiqnnXc1tIQkoXkH5EX5gSxtoi0Io6KceYf/9VuJCKcSowgYQ7x1MboMjyEMu0ddcy1Uyqch/S5e7wUN947DmXqxZU6iJo8Alj2vn9oHM+bbDuOoRBE6MNKUo+mGe+fLNL+HEikqh2yHr3iOMwrz 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: List-Subscribe: List-Unsubscribe: On 04.06.24 06:43, Byungchul Park wrote: > On Tue, Jun 04, 2024 at 10:53:48AM +0900, Byungchul Park wrote: >> On Mon, Jun 03, 2024 at 06:23:46AM -0700, Dave Hansen wrote: >>> On 6/3/24 02:35, Byungchul Park wrote: >>> ...> In luf's point of view, the points where the deferred flush should be >>>> performed are simply: >>>> >>>> 1. when changing the vma maps, that might be luf'ed. >>>> 2. when updating data of the pages, that might be luf'ed. >>> >>> It's simple, but the devil is in the details as always. >> >> Agree with that. >> >>>> All we need to do is to indentify the points: >>>> >>>> 1. when changing the vma maps, that might be luf'ed. >>>> >>>> a) mmap and munmap e.i. fault handler or unmap_region(). >>>> b) permission to writable e.i. mprotect or fault handler. >>>> c) what I'm missing. >>> >>> I'd say it even more generally: anything that installs a PTE which is >>> inconsistent with the original PTE. That, of course, includes writes. >>> But it also includes crazy things that we do like uprobes. Take a look >>> at __replace_page(). >>> >>> I think the page_vma_mapped_walk() checks plus the ptl keep LUF at bay >>> there. But it needs some really thorough review. >>> >>> But the bigger concern is that, if there was a problem, I can't think of >>> a systematic way to find it. >>> >>>> 2. when updating data of the pages, that might be luf'ed. >>>> >>>> a) updating files through vfs e.g. file_end_write(). >>>> b) updating files through writable maps e.i. 1-a) or 1-b). >>>> c) what I'm missing. >>> >>> Filesystems or block devices that change content without a "write" from >>> the local system. Network filesystems and block devices come to mind. >> >> AFAIK, every network filesystem eventully "updates" its connected local >> filesystem. It could be still handled at the point where updating the >> local file system. >> >>> I honestly don't know what all the rules are around these, but they >>> could certainly be troublesome. >>> >>> There appear to be some interactions for NFS between file locking and >>> page cache flushing. >>> >>> But, stepping back ... >>> >>> I'd honestly be a lot more comfortable if there was even a debugging LUF >> >> I'd better provide a method for better debugging. Lemme know whatever >> it is we need. >> >>> mode that enforced a rule that said: > > Do you means a debugging mode that can WARN or inform the situation that > we don't want? If yes, sure. Now that I get this, I will re-read all > you guys' talk. > In my opinion either for debugging, or for actually enforcing it at runtime. Whatever the cost of that would be needs to be determined. -- Cheers, David / dhildenb