Date: Wed, 3 Sep 2008 15:42:11 +0400 From: Igor Sysoev <is@rambler-co.ru> To: Sujit Karataparambil <sjt.kar@gmail.com> Cc: freebsd-stable@freebsd.org Subject: Re: vfs.ffs.rawreadahead Message-ID: <20080903114210.GC62541@rambler-co.ru> In-Reply-To: <921ca19c0809030433w50e16100rd624cdb4a2e4e947@mail.gmail.com> References: <20080903095352.GA62541@rambler-co.ru> <921ca19c0809030333u6accf415l80ec5bfb4a984ce1@mail.gmail.com> <20080903112512.GB62541@rambler-co.ru> <921ca19c0809030433w50e16100rd624cdb4a2e4e947@mail.gmail.com>
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On Wed, Sep 03, 2008 at 05:03:21PM +0530, Sujit Karataparambil wrote: > These are Journalling File System. Some thing like WAPBL > which stands for Write-Ahead Physical Block Logging. These > are built on Generic kernel components. vfs.ffs.rawreadahead as it may be seen from its name is read-ahead capability, but not write-ahead. And there is no any write-ahead related sysctl: #sysctl -a|grep ahead vfs.ffs.rawreadahead: 1 # > On 9/3/08, Igor Sysoev <is@rambler-co.ru> wrote: > > On Wed, Sep 03, 2008 at 04:03:59PM +0530, Sujit Karataparambil wrote: > > > > > The VFS was designed to be Object abtraction of the Berkeley Fast File System. > > > This has been since an terminology with journalling filesystem to have > > > functionality to added on request. > > > > In src/sys/ufs/ffs/ffs_rawread.c I see that rawreadahead is used. > > However, I do not understand whether rawreadahead starts a second > > parallel ahead disk transaction with supplied userland buffer or not. > > > > > > -- > > Igor Sysoev > > http://sysoev.ru/en/ > > > > > On 9/3/08, Igor Sysoev <is@rambler-co.ru> wrote: > > > > Hi, > > > > > > > > could anyone tell what does vfs.ffs.rawreadahead enable ? > > > > As I understand it's used in DIRECTIO code that allows read data > > > > directly to an userland buffer bypassing the buffer cache. > > > > What I can not understand where the read ahead data can be placed in ? > > > > > > > > > > > > -- > > > > Igor Sysoev > > > > http://sysoev.ru/en/ > > > > > -- > --linux(2.4/2.6),bsd(4.5.x+),solaris(2.5+) -- Igor Sysoev http://sysoev.ru/en/
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