Re: [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)

Vladimir V. Saveliev
2006-06-08T11:28:23Z

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.

> 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.