On Thu 30-03-17 15:53:35, Ilya Dryomov wrote: > On Thu, Mar 30, 2017 at 8:25 AM, Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > On Wed 29-03-17 16:25:18, Ilya Dryomov wrote: [...] > >> are you saying it's OK for a block > >> device to recurse back into the filesystem when doing I/O, potentially > >> generating more I/O? > > > > No, block device has to make a forward progress guarantee when > > allocating and so use mempools or other means to achieve the same. > > OK, let me put this differently. Do you agree that a block device > cannot make _any_ kind of progress guarantee if it does a GFP_KERNEL > allocation in the I/O path? yes that is correct. And the same is correct for GFP_NOIO allocations as well. -- Michal Hocko SUSE Labs