On Mon, May 25, 2020 at 10:28:06AM -0400, Peter Xu wrote: > On Mon, May 25, 2020 at 09:26:07AM -0300, Jason Gunthorpe wrote: > > On Sat, May 23, 2020 at 07:52:57PM -0400, Peter Xu wrote: > > > > > For what I understand now, IMHO we should still need all those handlings of > > > FAULT_FLAG_RETRY_NOWAIT like in the initial version. E.g., IIUC KVM gup will > > > try with FOLL_NOWAIT when async is allowed, before the complete slow path. I'm > > > not sure what would be the side effect of that if fault() blocked it. E.g., > > > the caller could be in an atomic context. > > > > AFAICT FAULT_FLAG_RETRY_NOWAIT only impacts what happens when > > VM_FAULT_RETRY is returned, which this doesn't do? > > Yes, that's why I think we should still properly return VM_FAULT_RETRY if > needed.. because IMHO it is still possible that the caller calls with > FAULT_FLAG_RETRY_NOWAIT. > > My understanding is that FAULT_FLAG_RETRY_NOWAIT majorly means: > > - We cannot release the mmap_sem, and, > - We cannot sleep Sleeping looks fine, look at any FS implementation of fault, say, xfs. The first thing it does is xfs_ilock() which does down_write(). I can't say when VM_FAULT_RETRY comes into play, but it is not so simple as just sleeping.. Jason
