Date: Fri, 18 Sep 2009 10:40:27 +0300 From: Kostik Belousov <kostikbel@gmail.com> To: d@delphij.net Cc: freebsd-hackers@freebsd.org Subject: Re: fcntl(F_RDAHEAD) Message-ID: <20090918074027.GI47688@deviant.kiev.zoral.com.ua> In-Reply-To: <4AB2B7A1.5000601@delphij.net> References: <20090917101526.GF57619@rambler-co.ru> <4AB2B7A1.5000601@delphij.net>
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[-- Attachment #1 --] On Thu, Sep 17, 2009 at 03:26:41PM -0700, Xin LI wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > Hi, Igor, > > Igor Sysoev wrote: > > Hi, > > > > nginx-0.8.15 can use completely non-blocking sendfile() using SF_NODISKIO > > flag. When sendfile() returns EBUSY, nginx calls aio_read() to read single > > byte. The first aio_read() preloads the first 128K part of a file in VM cache, > > however, all successive aio_read()s preload just 16K parts of the file. > > This makes non-blocking sendfile() usage ineffective for files larger > > than 128K. > > > > I've created a small patch for Darwin compatible F_RDAHEAD fcntl: > > > > fcntl(fd, F_RDAHEAD, preload_size) > > > > There is small incompatibilty: Darwin's fcntl allows just to enable/disable > > read ahead, while the proposed patch allows to set exact preload size. > > > > Currently the preload size affects vn_read() code path only and does not > > affect on sendfile() code path. However, it can be easy extended on > > sendfile() part too. The preload size is still limited by sysctl vfs.read_max. > > > > The patch is against FreeBSD 7.2 and was tested on FreeBSD 7.2-STABLE only. > > I have ported this as a patch against -HEAD (should apply on 8.0-R but > it's too late for us to add a new feature) plus a manual page entry > documenting the feature. > > I've used F_READAHEAD as the name, but reading the manual page, it looks > like we can just use F_RDAHEAD since Darwin seems to just distinguish 0 > and !=0 case so that programmers won't have to use #ifdef or something > else to get code working on different platform? What I dislike about the patch is the new kernel-private flag that is eaten from the open(2) flags namespace. We do already have FHASLOCK, so far the only such flag. [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (FreeBSD) iEYEARECAAYFAkqzOWsACgkQC3+MBN1Mb4jncwCg9zvfscnUBgH4Jsu1g/vRDRaJ En4An1ZLbdjiRLaEOqhvEUmRoCrP8pq3 =mP+3 -----END PGP SIGNATURE-----
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