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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1u7bva-00000009U9R-0oVY; Wed, 23 Apr 2025 15:22:22 +0000 Date: Wed, 23 Apr 2025 16:22:22 +0100 From: Matthew Wilcox To: Chuck Lever Cc: trondmy@kernel.org, linux-nfs@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org Subject: Re: [RFC PATCH 0/3] Initial NFS client support for RWF_DONTCACHE Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: ek54bif59p35jrnq9mfa3gahdaugadwg X-Rspamd-Queue-Id: 52A194000B X-Rspam-User: X-Rspamd-Server: rspam05 X-HE-Tag: 1745421744-820310 X-HE-Meta: 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 HCthiS5l eZJrMa5Tld4WMKtXeEtSb9cRhYZgXtvidwFY5kbDyiljDurAiRYd6L+Zvty3F7vovCXtUNFuJb0fpxJ4g1B9K9YXk/u3qFWpKdI6ssOfxVFTvJhNV5BBN9bS0msGU8OExRa8maKnja3wgz3KtB8cAaRdQa6pNS8RaXyCCV1IznqyGJXA2nR/2VwjX7wbKS0g3V7sY7y6kSBq3C7a4Wm9c6LIm9f+yHa0GPwDf/Mf8MtM3wic6T737uXE5xd5QlQE1KlFvFPkIjObSaHr8AFSk+GDGWORN8APsVLwLb5Q0Vkvy/JwDOb5HJZsimd4HaOXxc4/j92YcrNZrD3k7v2XWn6MGd4CkAyZ/Z4mXg2HvuUgDSuw= 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 Wed, Apr 23, 2025 at 10:38:37AM -0400, Chuck Lever wrote: > On 4/23/25 12:25 AM, trondmy@kernel.org wrote: > > From: Trond Myklebust > > > > The following patch set attempts to add support for the RWF_DONTCACHE > > flag in preadv2() and pwritev2() on NFS filesystems. > > Hi Trond- > > "RFC" in the subject field noted. > > The cover letter does not explain why one would want this facility, nor > does it quantify the performance implications. > > I can understand not wanting to cache on an NFS server, but don't you > want to maintain a data cache as close to applications as possible? If you look at the original work for RWF_DONTCACHE, you'll see this is the application providing the hint that it's doing a streaming access. It's only applied to folios which are created as a result of this access, and other accesses to these folios while the folios are in use clear the flag. So it's kind of like O_DIRECT access, except that it does go through the page cache so there's none of this funky alignment requirement on the userspace buffers.