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 <jack@xxxxxxxx> SUSE Labs, CR
