Re: A problem about DIRECT IO on ext3

[Jens Axboe]

On Wed, Aug 31 2005, Erik Mouw wrote:
> On Wed, Aug 31, 2005 at 10:07:45AM +0200, Jens Axboe wrote:
> > On Mon, Aug 29 2005, Erik Mouw wrote:
> > > There are four prerequisites for direct IO:
> > > - the file needs to be opened with O_DIRECT
> > > - the buffer needs to be page aligned (hint: use getpagesize() instead
> > >   of assuming that a page is 4k
> > > - reads and writes need to happen *in* multiples of the soft block size
> > > - reads and writes need to happen *at* multiples of the soft block size
> > 
> > Actually, the buffer only needs to be hard block size aligned, same goes
> > for the chunk size used for reads/writes.
> 
> OK, so that's different from 2.4 where reads/writes needed to be soft
> block aligned and buffers page aligned.

Yes, 2.6 has relaxed the restrictions there somewhat.

-- 
Jens Axboe

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