On Sun, Aug 30, 2020 at 04:28:00PM +0100, Christoph Hellwig wrote: > On Sun, Aug 30, 2020 at 09:09:02AM -0600, Jens Axboe wrote: > > On 8/30/20 12:26 AM, Christoph Hellwig wrote: > > > On Sat, Aug 29, 2020 at 10:51:11AM -0600, Jens Axboe wrote: > > >> We currently increment the task/vm counts when we first attempt to queue a > > >> bio. But this isn't necessarily correct - if the request allocation fails > > >> with -EAGAIN, for example, and the caller retries, then we'll over-account > > >> by as many retries as are done. > > >> > > >> This can happen for polled IO, where we cannot wait for requests. Hence > > >> retries can get aggressive, if we're running out of requests. If this > > >> happens, then watching the IO rates in vmstat are incorrect as they count > > >> every issue attempt as successful and hence the stats are inflated by > > >> quite a lot potentially. > > >> > > >> Add a bio flag to know if we've done accounting or not. This prevents > > >> the same bio from being accounted potentially many times, when retried. > > > > > > Can't the resubmitter just use submit_bio_noacct? What is the call > > > stack here? > > > > The resubmitter is way higher than that. You could potentially have that > > done in the block layer, but not higher up. > > > > The use case is async submissions, going through ->read_iter() again. > > Or ->write_iter(). > > But how does a bio flag help there? If we go through the file ops > again the next submission will be a new bio structure. Yeah, we also have use cases of stack bio variable. Thanks, Ming
