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AJvYcCU+FadVzraFTaJmqEu7ckoMlTmaHudZX2uLe7/+3SrBn2vvkbAatkMH+og7WD9tNPfCXbGTg764zw==@kvack.org X-Gm-Message-State: AOJu0YxyoEmBYV84yaSyFE95Oe4vP4EZHmJp4IRdfke21oxpFlWNtFHu puAlN6XZnTYZmyg4JGFwIwoUdVb6w2sYLQeeipjyuV0H9ICYMxnxXTLH3N6gbvJxXuQLwY3FvMa QKucnmu0TbZ6ZmVMEYzjpoYbTjpF09F4= X-Gm-Gg: ASbGncvLTal4oUK5BNvExsgzVyOMQBRCMRKJK77WzcHcP8cZqrncmr9zLmmOxX127fD bR7m98lrdzfweVssERdOO5IfiutwZcVpF12mEaPJeSs2qGFTkremY9cKuIYz2XqzmpKQKr3D6Ih T+ZnvC49so0e76+rgTLz0Ea09iY/cWMpq6OajMye4K1TD9tV+JyK5SR0SL69+VpwMoFg== X-Google-Smtp-Source: AGHT+IEVXR9+wlONFFF0pVmQeCbZZqUlGtHJsfnQn89wNLFqjyadnVgDXduPX3FgpzRh4Sq2aUSNlvX2yGgw+9F0I/g= X-Received: by 2002:a17:907:940e:b0:ad8:932e:77ba with SMTP id a640c23a62f3a-ade1aa06f9bmr166304966b.38.1749186295861; Thu, 05 Jun 2025 22:04:55 -0700 (PDT) MIME-Version: 1.0 References: <20250529111504.89912-1-kundan.kumar@samsung.com> <20250602141904.GA21996@lst.de> <20250603132434.GA10865@lst.de> <20250603140445.GA14351@lst.de> <20250603140513.GB14351@lst.de> In-Reply-To: <20250603140513.GB14351@lst.de> From: Kundan Kumar Date: Fri, 6 Jun 2025 10:34:42 +0530 X-Gm-Features: AX0GCFtEIAaI-VeodZn7ESl9-Aw4m_sJDaXecGQwiyGHiN7UJTfm9c_uBk6SQ-Q Message-ID: Subject: Re: [PATCH 00/13] Parallelizing filesystem writeback To: Christoph Hellwig Cc: Anuj gupta , "Anuj Gupta/Anuj Gupta" , Kundan Kumar , jaegeuk@kernel.org, chao@kernel.org, viro@zeniv.linux.org.uk, brauner@kernel.org, jack@suse.cz, miklos@szeredi.hu, agruenba@redhat.com, trondmy@kernel.org, anna@kernel.org, akpm@linux-foundation.org, willy@infradead.org, mcgrof@kernel.org, clm@meta.com, david@fromorbit.com, amir73il@gmail.com, axboe@kernel.dk, ritesh.list@gmail.com, djwong@kernel.org, dave@stgolabs.net, p.raghav@samsung.com, da.gomez@samsung.com, linux-f2fs-devel@lists.sourceforge.net, linux-fsdevel@vger.kernel.org, gfs2@lists.linux.dev, linux-nfs@vger.kernel.org, linux-mm@kvack.org, gost.dev@samsung.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 1076420009 X-Stat-Signature: c9snkrdszk441urb96hrmtamujxjqbj6 X-Rspam-User: X-HE-Tag: 1749186297-280974 X-HE-Meta: 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 jAhuP7ym 2yPjBLfDHyLundal0WTmcfb8abwBo89gFAl5muEIZRfI13wqVe3do6VZ/jQ== 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 Tue, Jun 3, 2025 at 7:35=E2=80=AFPM Christoph Hellwig wrote= : > > On Tue, Jun 03, 2025 at 04:04:45PM +0200, Christoph Hellwig wrote: > > On Tue, Jun 03, 2025 at 07:22:18PM +0530, Anuj gupta wrote: > > > > A mount option is about the worst possible interface for behavior > > > > that depends on file system implementation and possibly hardware > > > > chacteristics. This needs to be set by the file systems, possibly > > > > using generic helpers using hardware information. > > > > > > Right, that makes sense. Instead of using a mount option, we can > > > introduce generic helpers to initialize multiple writeback contexts > > > based on underlying hardware characteristics =E2=80=94 e.g., number o= f CPUs or > > > NUMA topology. Filesystems like XFS and EXT4 can then call these help= ers > > > during mount to opt into parallel writeback in a controlled way. > > > > Yes. A mount option might still be useful to override this default, > > but it should not be needed for the normal use case. > > .. actually a sysfs file on the bdi is probably the better interface > for the override than a mount option. Hi Christoph, Thanks for the suggestion =E2=80=94 I agree the default should come from a filesystem-level helper, not a mount option. I looked into the sysfs override idea, but one challenge is that nr_wb_ctx must be finalized before any writes occur. That leaves only a narrow window =E2=80=94 after the bdi is registered but before any inodes are dirtied =E2=80=94 where changing it is safe. This makes the sysfs knob a bit fragile unless we tightly guard it (e.g., mark it read-only after init). A mount option, even just as an override, feels simpler and more predictable, since it=E2=80=99s set before the FS becomes active.