linux-kernel - Re: [PATCH 4.4 48/76] libceph: force GFP

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Date:   Thu, 30 Mar 2017 15:59:34 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Ilya Dryomov <idryomov@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        stable@...r.kernel.org, Sergey Jerusalimov <wintchester@...il.com>,
        Jeff Layton <jlayton@...hat.com>, linux-xfs@...r.kernel.org
Subject: Re: [PATCH 4.4 48/76] libceph: force GFP_NOIO for socket allocations

On Thu 30-03-17 15:53:35, Ilya Dryomov wrote:
> On Thu, Mar 30, 2017 at 8:25 AM, Michal Hocko <mhocko@...nel.org> 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