vfs.ffs.rawreadahead

[Igor Sysoev]

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 at 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 at 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/