On Thu, Jan 25, 2024 at 9:11?AM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > > On Thu, Jan 25, 2024 at 09:09:44AM -0700, Jens Axboe wrote: > > On 1/25/24 1:10 AM, Christoph Hellwig wrote: > > > On Wed, Jan 24, 2024 at 08:40:28AM -0700, Jens Axboe wrote: > > >> On 1/24/24 2:39 AM, Christoph Hellwig wrote: > > >>> Make sure all in-line block layer submission runs in noio reclaim > > >>> context. This is a big step towards allowing GFP_NOIO, the other > > >>> one would be to have noio (and nofs for that matter) workqueues for > > >>> kblockd and driver internal workqueues. > > >> > > >> I really don't like adding this for no good reason. Who's doing non NOIO > > >> allocations down from this path? > > > > > > If there is a non-NOIO allocation right now that would be a bug, > > > although I would not be surprised if we had a few of them. > > > > > > The reason to add this is a different one: The MM folks want to > > > get rid of GFP_NOIO and GFP_NOFS and replace them by these context. > > > > > > And doing this in the submission path and kblockd will cover almost > > > all of the noio context, with the rest probably covered by other > > > workqueues. And this feels a lot less error prone than requiring > > > every driver to annotate the context in their submission routines. > > > > I think it'd be much better to add a DEBUG protected aid that checks for > > violating allocations. Nothing that isn't buggy should trigger this, > > right now, and then we could catch problems if there are any. If we do > > the save/restore there and call it good, then we're going to be stuck > > with that forever. Regardless of whether it's actually needed or not. > > Nono, you don't understand. The plan is to remove GFP_NOIO > entirely. Allocations should be done with GFP_KERNEL while under a > memalloc_noio_save(). I do understand, but thanks for the vote of confidence. Place the save/restore higher up, most likely actual IO submission isn't going to be the only (or even major) allocation potentially needed for the IO. -- Jens Axboe
