On Wed 01-03-17 07:38:57, Christoph Hellwig wrote:
> On Tue, Feb 28, 2017 at 07:46:06PM -0800, Matthew Wilcox wrote:
> > Ugh, this is pretty inefficient. If that's all you want to know, then
> > using the radix tree directly will be far more efficient than spinning
> > up all the pagevec machinery only to discard the pages found.
> >
> > But what's going to kick these pages out of cache? Shouldn't we rather
> > find the pages, kick them out if clean, start writeback if not, and *then*
> > return -EAGAIN?
> >
> > So maybe we want to spin up the pagevec machinery after all so we can
> > do that extra work?
>
> As pointed out in the last round of these patches I think we really
> need to pass a flags argument to filemap_write_and_wait_range to
> communicate the non-blocking nature and only return -EAGAIN if we'd
> block. As a bonus that can indeed start to kick the pages out.
Aren't flags to filemap_write_and_wait_range() unnecessary complication?
Realistically, most users wanting performance from AIO DIO so badly that
they bother with this API won't have any pages to write / evict. If they do
by some bad accident, they can fall back to standard "blocking" AIO DIO.
So I don't see much value in teaching filemap_write_and_wait_range() about
a non-blocking mode...
Honza
--
Jan Kara <[email protected]>
SUSE Labs, CR
