[lkml]   [2004]   [May]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: Random file I/O regressions in 2.6
On Mon, 2004-05-03 at 14:37, Peter Zaitsev wrote:
> On Mon, 2004-05-03 at 13:57, Andrew Morton wrote:
> > Ram Pai <> wrote:
> > >
> > > > The place which needs attention is handle_ra_miss(). But first I'd like to
> > > > reacquaint myself with the intent behind the lazy-readahead patch. Was
> > > > never happy with the complexity and special-cases which that introduced.
> > >
> > > lazy-readahead has no role to play here.
> >
> Andrew,
> Could you please clarify how this things become to be dependent on
> read-ahead at all.
> At my understanding read-ahead it to catch sequential (or other) access
> pattern and do some advance reading, so instead of 16K request we do
> 128K request, or something similar.
> But how could read-ahead disabled end up in 16K request converted to
> several sequential synchronous 4K requests ?

When the readahead window gets closed,the code goes into slow-read mode.
In this mode, all requests are broken to page-size. Hence a 16k request
gets broken into 4 4K-requests. This continues to the point where
enough number of sequential i/os are requested(i.e around ra->ra_pages
number of pages), at which point the readahead window gets

Looking at it the other way, without readahead code, all requests
satisfied through 4k i/os. Readahead helps in generating larger size


To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

 \ /
  Last update: 2005-03-22 14:02    [W:0.076 / U:1.384 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site