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smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=sk.com; spf=pass smtp.mailfrom=sk.com; arc=none smtp.client-ip=166.125.252.92 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=sk.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=sk.com X-AuditID: a67dfc5b-c45ff70000001609-d8-691e784bd858 Date: Thu, 20 Nov 2025 11:09:09 +0900 From: Byungchul Park To: Matthew Wilcox Cc: linux-kernel@vger.kernel.org, kernel_team@skhynix.com, torvalds@linux-foundation.org, damien.lemoal@opensource.wdc.com, linux-ide@vger.kernel.org, adilger.kernel@dilger.ca, linux-ext4@vger.kernel.org, mingo@redhat.com, peterz@infradead.org, will@kernel.org, tglx@linutronix.de, rostedt@goodmis.org, joel@joelfernandes.org, sashal@kernel.org, daniel.vetter@ffwll.ch, duyuyang@gmail.com, johannes.berg@intel.com, tj@kernel.org, tytso@mit.edu, david@fromorbit.com, amir73il@gmail.com, gregkh@linuxfoundation.org, kernel-team@lge.com, linux-mm@kvack.org, akpm@linux-foundation.org, mhocko@kernel.org, minchan@kernel.org, hannes@cmpxchg.org, vdavydov.dev@gmail.com, sj@kernel.org, jglisse@redhat.com, dennis@kernel.org, cl@linux.com, penberg@kernel.org, rientjes@google.com, vbabka@suse.cz, ngupta@vflare.org, linux-block@vger.kernel.org, josef@toxicpanda.com, linux-fsdevel@vger.kernel.org, jack@suse.cz, jlayton@kernel.org, dan.j.williams@intel.com, hch@infradead.org, djwong@kernel.org, dri-devel@lists.freedesktop.org, rodrigosiqueiramelo@gmail.com, melissa.srw@gmail.com, hamohammed.sa@gmail.com, harry.yoo@oracle.com, chris.p.wilson@intel.com, gwan-gyeong.mun@intel.com, max.byungchul.park@gmail.com, boqun.feng@gmail.com, longman@redhat.com, yunseong.kim@ericsson.com, ysk@kzalloc.com, yeoreum.yun@arm.com, netdev@vger.kernel.org, matthew.brost@intel.com, her0gyugyu@gmail.com, corbet@lwn.net, catalin.marinas@arm.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, luto@kernel.org, sumit.semwal@linaro.org, gustavo@padovan.org, christian.koenig@amd.com, andi.shyti@kernel.org, arnd@arndb.de, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, rppt@kernel.org, surenb@google.com, mcgrof@kernel.org, petr.pavlu@suse.com, da.gomez@kernel.org, samitolvanen@google.com, paulmck@kernel.org, frederic@kernel.org, neeraj.upadhyay@kernel.org, joelagnelf@nvidia.com, josh@joshtriplett.org, urezki@gmail.com, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, qiang.zhang@linux.dev, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, chuck.lever@oracle.com, neil@brown.name, okorniev@redhat.com, Dai.Ngo@oracle.com, tom@talpey.com, trondmy@kernel.org, anna@kernel.org, kees@kernel.org, bigeasy@linutronix.de, clrkwllms@kernel.org, mark.rutland@arm.com, ada.coupriediaz@arm.com, kristina.martsenko@arm.com, wangkefeng.wang@huawei.com, broonie@kernel.org, kevin.brodsky@arm.com, dwmw@amazon.co.uk, shakeel.butt@linux.dev, ast@kernel.org, ziy@nvidia.com, yuzhao@google.com, baolin.wang@linux.alibaba.com, usamaarif642@gmail.com, joel.granados@kernel.org, richard.weiyang@gmail.com, geert+renesas@glider.be, tim.c.chen@linux.intel.com, linux@treblig.org, alexander.shishkin@linux.intel.com, lillian@star-ark.net, chenhuacai@kernel.org, francesco@valla.it, guoweikang.kernel@gmail.com, link@vivo.com, jpoimboe@kernel.org, masahiroy@kernel.org, brauner@kernel.org, thomas.weissschuh@linutronix.de, oleg@redhat.com, mjguzik@gmail.com, andrii@kernel.org, wangfushuai@baidu.com, linux-doc@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org, linux-i2c@vger.kernel.org, linux-arch@vger.kernel.org, linux-modules@vger.kernel.org, rcu@vger.kernel.org, linux-nfs@vger.kernel.org, linux-rt-devel@lists.linux.dev Subject: Re: [PATCH v17 44/47] dept: introduce APIs to set page usage and use subclasses_evt for the usage Message-ID: <20251120020909.GA78650@system.software.com> References: <20251002081247.51255-1-byungchul@sk.com> <20251002081247.51255-45-byungchul@sk.com> <20251119105312.GA11582@system.software.com> Precedence: bulk X-Mailing-List: rcu@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) X-Brightmail-Tracker: H4sIAAAAAAAAA02SbUxTZxTH89znvtHY5VodPlr0Qw3OsMgc0eQ4nXG+5SaGZGbEKH7AZlzl zvKyoghLyHDyJjLEbs5YkJXiFGhVqGjQlQywVKGCkBGs8qJWdDKYCgM2KVR7NUa//c45//zO +XB4rOliFvBy0j7JmKQ36FgVrfpnlnXZlvRF8vKcpsXQc7CRhnsT+QhmTG4OXja4EfzSZcJg rztIwZnBAAWDjXkI/O23MJw43ongSU2wrHMPIOieeMaC5YcGBg5VXGCha3iaApsjGjzFVgpO DLHgqzQHlZZkcNv+4qD/6HEa7IWPMZTnnqbhz6ulLBTWXGJgwP6SgayS/xjwuG/Q8OC+l4HO Yz8y4C1+hMBtCYWx05M05P4bYOC38acY2ks6GOgr+puGaxMjFEz11zPQY/qVhZzCFxzkuyYx ZPetBP//wQ3jtmoWSloGuHXLRXuZHYn+KRMSr408w2KblYhXzP2ceLEyQqxwDlHi3eHPRUf1 YVZ0jJk4sdz/BIt9PU5WfNrRwYlXHqwSy1q3in+csnNfzo9VrYmXDHKaZPxk7S5VwvSUhU5x hKVX3DZTWSg7tACF8ERYQYbzc3AB4l/zzexMpU0L4cRTcJVVmBU+Il7vi9eRucJSMlIXVYBU PBasWnKurYlRMnMEA5l0necUVgtAAlWVSAlphN8R6c6tZd4MZpPWk4O0wliIIN7AEKVIsaAl ZwO80g4JnnDHmocV/lBYTBovX6cUDxF8IcSWX4Xf3DyfNFV66WIkmN/Tmt/Tmt9pLQhXI42c lJaolw0rIhMykuT0yK+TEx0o+GhnMqd31qOxzq+akcAj3Sz1dvdCWcPo01IzEpsR4bFurjr8 izBZo47XZ3wnGZPjjPsNUmoz0vK0bp46avJAvEbYo98n7ZWkFMn4dkrxIQuyUFlk9M9FTqdP U1oek9Kb+Xx0z8PajxP8sRfvdfpu7NUOy492f190eEtey5HN3VMnTZtuJtpdCz2rDgzmtIbH xjlHtfPa1jRs9NhGo6P6zrLrj9Z/UPst+qZ+w/MY90+qbb0PQ9t3tBhcYZ5t4zMzGfzqXqev dPO6blfVkoFa/BldGqOjUxP0n0ZgY6r+FZMm1P9kAwAA X-Brightmail-Tracker: H4sIAAAAAAAAA02Sb0xbZRTGfe/73j80llwrsuvYNOmCkiVDIS4eJzH6aTdLtqgxcUGJa8aN 3LQU1jIEsyVlpUJQJ5QUspbNWlxFYIy1SGSk2LFRMxjbKtOhDgFTYQQYyaRs0NLaG2Pcl5Pf Oc/znJwPh8OaOL2Vk40VksmoM2gZFVEdeNW6a1/VM/KLQ50F8EtNkEB0tZ5A2/luBup9p2i4 2dOFYDpaj+BBzIXBNpAksGkPsbC6/jsLyUAIQUvYjqG7r4aCv3sTDCxevo/AMRthoHWhhsCK 9zMEzjkXCwsje2F5epCG5NQ8BbfXlhB4IwkKIsE6BJstevjS42cgNn4DQ6vjJoKvZqcw3O1N iX2hPxAEOk4w8FfjdxgmIulwK7rCwFXHpwwsh9souNfLgPtEgIbTLjsCa/t5BlpO+wgMzFxk IbwYp+BOi52CLt9+mPbOERhr9FCp+1KuC1vA1WqlUuUuBY5zgxSseztZuNZ+h4DXkg2u8Qka /uxwshCfzYOkuwxCXfMsTH3hINCzfIN+3YHEB7aTROz091Oi7adNRuw+043E2IYdiatnrVi0 Nabay0srWKz1fySeHVtixI3oz4wYWHMTcdQjiE3ju8QB5xQr1g79xr65p1BVUCwZ5ErJ9MJr h1Ql8Q03Kfdtq2q/7aQsqDazAXGcwL8kXKs93oDSOMJnC2MNFxmFGf55YXJyHSuWDD5HWOrL b0AqDvOeLOHc6CVa8TzJG4S1Kz2swmoehMS3HUgxafhBJNz65AL9r/CEcPVUhCiM+Z3CZGKB UpZiPkv4JsEp47TUCb966rDCT/E7hGD/j1QjUjsfSTsfSTv/T7sR7kQZsrGyVCcbduea9SXV Rrkq93BZqQ+lftJ7PN70PVqd2DuMeA5pH1cfDG2XNbSu0lxdOowEDmsz1NlvbJM16mJd9ceS qewD01GDZB5GWRzRblHve1c6pOE/1FVIekkql0z/qRSXttWCrhx772hBRWHmyz35+R7LTPMr 6Q99b0dzFv30wPD8Y+k1Ujhel/t+buERlz6WbWwK0qEiOJPjj+lHdrxT2mxJPHvP5ZH3+0bn 8GDeTODwyeofirZfPxI8WJ9sO0bfL+6zft1sGhop6Ch/eo9Fbb1kux7+fPfD/oTkKyKxt57L PKAl5hJd3k5sMuv+AScIleSPAwAA X-CFilter-Loop: Reflected On Wed, Nov 19, 2025 at 02:37:17PM +0000, Matthew Wilcox wrote: > On Wed, Nov 19, 2025 at 07:53:12PM +0900, Byungchul Park wrote: > > On Thu, Oct 02, 2025 at 05:12:44PM +0900, Byungchul Park wrote: > > > False positive reports have been observed since dept works with the > > > assumption that all the pages have the same dept class, but the class > > > should be split since the problematic call paths are different depending > > > on what the page is used for. > > > > > > At least, ones in block device's address_space and ones in regular > > > file's address_space have exclusively different usages. > > > > > > Thus, define usage candidates like: > > > > > > DEPT_PAGE_REGFILE_CACHE /* page in regular file's address_space */ > > > DEPT_PAGE_BDEV_CACHE /* page in block device's address_space */ > > > DEPT_PAGE_DEFAULT /* the others */ > > > > 1. I'd like to annotate a page to DEPT_PAGE_REGFILE_CACHE when the page > > starts to be associated with a page cache for fs data. > > > > 2. And I'd like to annotate a page to DEPT_PAGE_BDEV_CACHE when the page > > starts to be associated with meta data of fs e.g. super block. > > > > 3. Lastly, I'd like to reset the annotated value if any, that has been > > set in the page, when the page ends the assoication with either page > > cache or meta block of fs e.g. freeing the page. > > > > Can anyone suggest good places in code for the annotation 1, 2, 3? It'd > > be totally appreciated. :-) > > I don't think it makes sense to track lock state in the page (nor > folio). Partly bcause there's just so many of them, but also because > the locking rules don't really apply to individual folios so much as > they do to the mappings (or anon_vmas) that contain folios. Thank you for the suggestion! Since two folios associated to different mappings might appear in the same callpath that usually be classified to a single class, I need to think how to reflect the suggestion. I guess you wanted to tell me a folio can only be associated to a single mapping at once. Right? If so, sure, I should reflect it. > If you're looking to find deadlock scenarios, I think it makes more > sense to track all folio locks in a given mapping as the same lock > type rather than track each folio's lock status. > > For example, let's suppose we did something like this in the > page fault path: > > Look up and lock a folio (we need folios locked to insert them into > the page tables to avoid a race with truncate) > Try to allocate a page table > Go into reclaim, attempt to reclaim a folio from this mapping > > We ought to detect that as a potential deadlock, regardless of which > folio in the mapping we attempt to reclaim. So can we track folio Did you mean 'regardless' for 'potential' detection, right? > locking at the mapping/anon_vma level instead? Piece of cake. Even though it may increase the number of DEPT classes, I hope it will be okay. I just need to know the points in code where folios start/end being associated to their specific mappings. Byungchul > --- > > My current understanding of folio locking rules: > > If you hold a lock on folio A, you can take a lock on folio B if: > > 1. A->mapping == B->mapping and A->index < B->index > (for example writeback; we take locks on all folios to be written > back in order) > 2. !S_ISBLK(A->mapping->host) and S_ISBLK(B->mapping->host) > 3. S_ISREG(A->mapping->host) and S_ISREG(B->mapping->host) with > inode_lock() held on both and A->index < B->index > (the remap_range code)