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Mon, 17 Jun 2024 17:50:29 +0800 (CST) Subject: Re: [PATCH] mm/gup: don't check page lru flag before draining it To: David Hildenbrand , Matthew Wilcox Cc: Baolin Wang , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, liuzixing@hygon.cn References: <0d7a4405-9a2e-4bd1-ba89-a31486155233@redhat.com> <776de760-e817-43b2-bd00-8ce96f4e37a8@redhat.com> <7063920f-963a-4b3e-a3f3-c5cc227bc877@redhat.com> <48150a28-ed48-49ff-9432-9cd30cda4da4@linux.alibaba.com> <11ef3deb-d1e3-46d5-97ed-9ba3c1fbbba9@redhat.com> <697a9bc2-a655-4035-aa5e-7d3acb23e79d@redhat.com> <3a368e38-a4cb-413e-a6d9-41c6b3dbd5ae@redhat.com> <48fb0e58-16d1-7956-cf35-74741826617a@126.com> <617f9e36-9334-4630-a6b9-473f2dd570d4@redhat.com> <8351052a-5c21-c383-544b-3166e883587c@126.com> From: yangge1116 Message-ID: <7b69abe5-3782-965c-ec82-5baef84e2d06@126.com> Date: Mon, 17 Jun 2024 17:50:27 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-CM-TRANSID:_____wD331jkBnBm1R1bCw--.7695S2 X-Coremail-Antispam: 1Uf129KBjvJXoW7Cw17tFW8KF4xXFy3uryDKFg_yoW8trykpF yUKF9rKF4qkryqkFnFqr17ArsYy3yrXFy5ZFWxJFy7CF4qqF15KrW8ta15uFy3Jr4Fgr1I ka12q3WfWF1UAaDanT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDUYxBIdaVFxhVjvjDU0xZFpf9x07b8PEfUUUUU= X-Originating-IP: [118.242.3.34] X-CM-SenderInfo: 51dqwwjhrrila6rslhhfrp/1tbiWRIBG2VLaxbqAAAAso X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 8219040017 X-Stat-Signature: fn6fjykatooq3p8yd8ewn5hf1rqw35on X-Rspam-User: X-HE-Tag: 1718617858-20376 X-HE-Meta: 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 K+Cf2eGq xXzWDcp55UE+R5+WkMixeinIL2SyXOeXm8R6AHykhw4mWyJrBqu8MI29egKo0g+RCbfqY8wNyM1TJMuezjo1hPxWGyoTxUAw24Qgmhx6VHJIcvSQIVMfbjmGT8ZlmpAc6ZQAvfbOPwefjQOeMdYrwLqruoimcv9bTGhZFj/embRmtHSf/GJgzFRbPOF689PNUQvZZ0r5Lxz3J28Ou6ytM9ybuUL7R7DiTaOAGT2g+m3p1bPww7KEJbB65GIJ+Ac8mXF8Fw8FXR+mUS5MJi3B8tKwZI7UgabedhiQs1mOTvSrY4ID2vMn+PYVQeglf0Af8g2XqKrjpWMEtF/yN44xxpfIpE+sa80bJzyJiwcY+LYu5qBiXE5LmhRXiCxkdygIzxBKQajms88EABQU= 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: 在 2024/6/12 下午3:32, David Hildenbrand 写道: > On 11.06.24 13:20, yangge1116 wrote: >> >> >> 在 2024/6/9 上午12:03, David Hildenbrand 写道: >>> On 08.06.24 17:15, Matthew Wilcox wrote: >>>> On Sat, Jun 08, 2024 at 12:38:49PM +0800, yangge1116 wrote: >>>>> Can we add a PG_lru_batch flag to determine whether a page is in lru >>>>> batch? >>>>> If we can, seems this problem will be easier. >>>> >>>> Page flags are in short supply.  You'd need a really good >>>> justification. >>>> >>> >>> A flag would not be able to handle the "part of multiple LRU batches" >>> that should currently possible (when to clear the flag?). Well, if we >>> have to keep supporting that. If we only to be part in a single LRU >>> batch, a new flag could work and we could still allow isolating a folio >>> from LRU while in some LRU batch. >> >> Yes, before adding a folio to LRU batch, check whether the folio has >> been added. Add the folio to LRU batch only if the folio has not been >> added. >> >>> >>> If we could handle it using the existing flags, that would of course be >>> better (wondering if we could store more information in the existing >>> flags by using a different encoding for the different states). >> >> If a folio contains more than one page, the folio will not be added to >> LRU batch. Can we use folio_test_large(folio) to filter? >> >> if (!folio_test_large(folio) && drain_allow) { >>     lru_add_drain_all(); >>     drain_allow = false; >> } > > I think we should do better than this, and not do arbitrary > lru_add_drain_all() calls. > Thanks, I've got another idea. If we add GUP_PIN_COUNTING_BIAS to folio's ref count before adding to LRU batch, we can use folio_maybe_dma_pinned(folio) to check whether the folio is in LRU batch. I wonder if it's feasible? static void folio_batch_add_and_move(struct folio_batch *fbatch, struct folio *folio, move_fn_t move_fn) { if (!folio_test_large(folio)) { folio_ref_add(folio, GUP_PIN_COUNTING_BIAS); if (folio_batch_add(fbatch, folio) && !lru_cache_disabled()) return; } folio_batch_move_lru(fbatch, move_fn); } if (!folio_test_large(folio) && folio_maybe_dma_pinned(folio) && drain_allow) { lru_add_drain_all(); drain_allow = false; }