On Tue 10-05-22 13:16:30, Stefan Roesch wrote: > On 5/10/22 2:50 AM, Jan Kara wrote: > > I know that you're using fields in task_struct to propagate the delay info. > > But IMHO that is unnecessary (although I don't care too much). Instead we > > could factor out a variant of balance_dirty_pages() that returns 'pause' to > > sleep, 0 if no sleeping needed. Normal balance_dirty_pages() would use this > > for pause calculation, places wanting async throttling would only get the > > pause to sleep. So e.g. iomap_write_iter() would then check and if returned > > pause is > 0, it would abort the loop similary as we'd abort it for any > > other reason when NOWAIT write is aborted because we need to sleep. Iouring > > code then detects short write / EAGAIN and offloads the write to the > > workqueue where normal balance_dirty_pages() can sleep as needed. > > > > This will make sure dirty limits are properly observed and we don't need > > that much special handling for it. > > > > I like the idea of factoring out a function out balance_dirty_pages(), however > > I see two challenges: > - the write operation has already completed at this point, > - so we can't really sleep on its completion in the io-worker in io-uring > - we don't know how long to sleep in io-uring > > Currently balance_dirty_pages_ratelimited() is called at the end of the > function iomap_write_iter(). If the function > balance_dirty_pages_ratelimited() would instead be called at the > beginning of the function iomap_write_iter() we could return -EAGAIN and > then complete it in the io-worker. Well, we call balance_dirty_pages_ratelimited() after each page. So it does not really matter much if the sleep is pushed to happen one page later. balance_dirty_pages_ratelimited() does ratelimiting of when balance_dirty_pages() are called so we have to make sure current->nr_dirtied is not zeroed out before we really do wait (because that is what determines whether we enter balance_dirty_pages() and how long we sleep there) but looking at the code that should work out just fine. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
