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[49.179.32.121]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-72c6d00b5aasm6614155a12.83.2024.07.02.06.04.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 02 Jul 2024 06:04:51 -0700 (PDT) Received: from dave by dread.disaster.area with local (Exim 4.96) (envelope-from ) id 1sOdBh-001WSP-0j; Tue, 02 Jul 2024 23:04:49 +1000 Date: Tue, 2 Jul 2024 23:04:49 +1000 From: Dave Chinner To: Trond Myklebust Cc: "snitzer@kernel.org" , "bfoster@redhat.com" , "linux-nfs@vger.kernel.org" , "linux-xfs@vger.kernel.org" Subject: Re: [PATCH v2] xfs: enable WQ_MEM_RECLAIM on m_sync_workqueue Message-ID: References: Precedence: bulk X-Mailing-List: linux-nfs@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: On Tue, Jul 02, 2024 at 12:33:53PM +0000, Trond Myklebust wrote: > On Mon, 2024-07-01 at 10:13 -0400, Mike Snitzer wrote: > > On Mon, Jul 01, 2024 at 09:46:36AM +1000, Dave Chinner wrote: > > > IMO, the only sane way to ensure this sort of nested "back-end page > > > cleaning submits front-end IO filesystem IO" mechanism works is to > > > do something similar to the loop device. You most definitely don't > > > want to be doing buffered IO (double caching is almost always bad) > > > and you want to be doing async direct IO so that the submission > > > thread is not waiting on completion before the next IO is > > > submitted. > > > > Yes, follow-on work is for me to revive the directio path for localio > > that ultimately wasn't pursued (or properly wired up) because it > > creates DIO alignment requirements on NFS client IO: > > https://git.kernel.org/pub/scm/linux/kernel/git/snitzer/linux.git/commit/?h=nfs-localio-for-6.11-testing&id=f6c9f51fca819a8af595a4eb94811c1f90051eab I don't follow - this is page cache writeback. All the write IO from the bdi flusher thread should be page aligned, right? So why does DIO alignment matter here? > > But underlying filesystems (like XFS) have the appropriate checks, we > > just need to fail gracefully and disable NFS localio if the IO is > > misaligned. > > > > Just a reminder to everyone that this is replacing a configuration > which would in any case result in double caching, because without the > localio change, it would end up being a loopback mount through the NFS > server. Sure. That doesn't mean double caching is desirable and it's something we try should avoid if we trying to design a fast server bypass mechanism. -Dave. -- Dave Chinner david@fromorbit.com