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SubjectRe: [PATCH] updated reiser4 - reduced cpu usage for writes by writing more than 4k at a time (has implications for generic write code and eventually for the IO layer)
On Thu, Jun 08 2006, Vladimir V. Saveliev wrote:
> Hello
>
> On Thu, 2006-06-08 at 13:00 +0200, Jens Axboe wrote:
> > On Wed, May 24 2006, Hans Reiser wrote:
> > > Tom Vier wrote:
> > >
> > > >On Tue, May 23, 2006 at 01:14:54PM -0700, Hans Reiser wrote:
> > > >
> > > >
> > > >>underlying FS can be improved. Performance results show that the new
> > > >>code consumes 40% less CPU when doing "dd bs=1MB ....." (your hardware,
> > > >>and whether the data is in cache, may vary this result). Note that this
> > > >>has only a small effect on elapsed time for most hardware.
> > > >>
> > > >>
> > > >
> > > >Write requests in linux are restricted to one page?
> > > >
> > > >
> > > >
> > > It may go to the kernel as a 64MB write, but VFS sends it to the FS as
> > > 64MB/4k separate 4k writes.
> >
> > Nonsense,
>
> Hans refers to generic_file_write which does
> prepare_write
> copy_from_user
> commit_write
> for each page.

Provide your own f_op->write() ?

> > there are ways to get > PAGE_CACHE_SIZE writes in one chunk.
> > Other file systems have been doing it for years.
> >
>
> Would you, please, say more about it.

Use writepages?

--
Jens Axboe

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