On 4/12/07, Roman Zippel <[email protected]> wrote:
Hi,
On Thu, 12 Apr 2007, Christoph Hellwig wrote:
> On Wed, Apr 11, 2007 at 07:49:38PM -0700, Nate Diller wrote:
> > read_mapping_page_async() is going away, so convert its only user to
> > read_mapping_page(). This change has not been benchmarked, however, in
> > order to get real parallelism this wants something completely different,
> > like __do_page_cache_readahead(), which is not currently exported.
>
> Why is read_mapping_page_async going away? This probably needs a lot more
> testing, and I'd be much happier if you split it out of the series and
> sent it separately at the end.
That function wasn't fully async anyway, as it would often sleep in
lock_page(). AFAICT only in the special case of a partial written page
would this function return a not yet uptodate page.
yes, exactly, the structure of read_cache_page() and friends is
totally not appropriate for doing async I/O to more than one page at a
time, and the whole point of the special treatment in cramfs was to
read 4 pages at once rather than synchronously reading each of the 4
seperately. read_cache_page_async() is totally wrong for that use,
its purpose would be to get a reference to a single page that is
likely to be in cache already without having to take the page_lock.
Turns out nobody needs to do that, so there's no point in keeping it
around.
If the performance gain of reading all 4 pages at once would be worth
the effort, this code should be using __do_page_cache_readahead().
That function allocates all the pages first, then reads them in
asynchronously as a group. It is currently not exported.
NATE
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