Re: [PATCH 4.4 48/76] libceph: force GFP_NOIO for socket allocations

[Michal Hocko]

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