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bh=JtPiOgRKCd1DVDF6rMovizquEnEA+3526ZmAhvq4I4g=; b=UvBSJp/Kpf8xK/+HXVwSIaVAguYnNe6G6FhThaS7h+aviLivaQGiYnKSvGXBY4Jjvy t2UpIQ3shO3GmLDwwZ3izOEHtytIQVySapjBN/L4i+U+xE3JDTXrg8SlAHvt4tDxlwca dZPA0XIiOKrrkalJGgB4jSuSe6YEoJrZXXdmi0LYxtqM5LnNc8uESAT+PtoBcy58Bg9I XUfU9b009gwgWm2rss37mGTM8dqRHCGxjDhyTVakU3WnpLu9pM4xsbBVXykl5C9rXJln tXHoU7/KUg0gpY6pUcs5blh9qxEgX9s3N4TrDLvYHjURgketLwxFnwHFMrJQ2+1IXna8 F0rQ== X-Gm-Message-State: APjAAAWrJLkMH91bKncvMrsxZxSl5XHPnYQBRMVx5P3t4abqTkuo3FON fVcEnXbqKdhHiQX6TrTmLsLXvaJq1Ai0JB9lH/wM+CRZ3Bs0mz7MABMbWhoq+2invIGSTgTM+fW X/MsE7dLr5w3dfT1vOckaWtfCUdjSyf8= X-Received: by 2002:a05:6602:24c6:: with SMTP id h6mr2894556ioe.273.1578669200157; Fri, 10 Jan 2020 07:13:20 -0800 (PST) X-Google-Smtp-Source: APXvYqxzXwE1B5T4Hrw3Xvb8tst9a6CtwiW/BIwACUVb/NtO/ub9XHZnZIRPaGMz5SCQqXC0DHe3UojrLu8FYQTAgyk= X-Received: by 2002:a05:6602:24c6:: with SMTP id h6mr2894533ioe.273.1578669199894; Fri, 10 Jan 2020 07:13:19 -0800 (PST) MIME-Version: 1.0 References: <20191212163904.159893-1-dgilbert@redhat.com> <20191212163904.159893-69-dgilbert@redhat.com> <20200107112316.GL3368802@redhat.com> <20200110150447.GH3901@work-vm> In-Reply-To: <20200110150447.GH3901@work-vm> From: Miklos Szeredi Date: Fri, 10 Jan 2020 16:13:08 +0100 Message-ID: Subject: Re: [PATCH 068/104] virtiofsd: passthrough_ll: control readdirplus To: "Dr. David Alan Gilbert" X-MC-Unique: xfoZGW-yOnyxRU2T4pQZyw-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 205.139.110.120 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: =?UTF-8?Q?Daniel_P=2E_Berrang=C3=A9?= , qemu-devel@nongnu.org, Stefan Hajnoczi , Vivek Goyal Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, Jan 10, 2020 at 4:04 PM Dr. David Alan Gilbert wrote: > > * Daniel P. Berrang=C3=A9 (berrange@redhat.com) wrote: > > On Thu, Dec 12, 2019 at 04:38:28PM +0000, Dr. David Alan Gilbert (git) = wrote: > > > From: Miklos Szeredi > > > > > > > What is readdirplus and what do we need a command line option to > > control it ? What's the user benefit of changing the setting ? > > cc'ing Miklos who understands this better than me. > > My understanding is that readdirplus is a heuristic inherited from NFS > where when you iterate over the directory you also pick up stat() data > for each entry in the directory. You then cache that stat data > somewhere. > The Plus-ness is that a lot of directory operations involve you stating > each entry (e.g. to figure out if you can access it etc) so rolling it > into one op avoids the separate stat. The unplus-ness is that it's an > overhead and I think changes some of the caching behaviour. Yeah, so either may give better performance and it's hard to pick a clear winner. NFS also has an option to control this. Thanks, Miklos