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/
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. Thanks, Sujit 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/ > _______________________________________________ > freebsd-stable@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-stable > To unsubscribe, send any mail to "freebsd-stable-unsubscribe@freebsd.org" >-- --linux(2.4/2.6),bsd(4.5.x+),solaris(2.5+)
On Wed, Sep 03, 2008 at 01:53:52PM +0400, Igor Sysoev 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 ?The operation of the ffs_rawread is more accurately described as bypassing the page cache. It creates the physical buffer that maps the user pages. The readahead is performed only when the supplied user memory region is bigger then blocksize. In this case, two reads are performed simultaneously, with both buffers mapping consequent blocks from user-supplied buffers. The read operation looks like footsteps. -------------- next part -------------- A non-text attachment was scrubbed... Name: not available Type: application/pgp-signature Size: 195 bytes Desc: not available Url : http://lists.freebsd.org/pipermail/freebsd-stable/attachments/20080903/3e07deb6/attachment.pgp