linux-kernel - Re: [GIT PULL] Please pull NFS client fixes for 4.12

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Message-ID: <20170511075910.GD26782@dhcp22.suse.cz>
Date:   Thu, 11 May 2017 09:59:11 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Nikolay Borisov <n.borisov.lkml@...il.com>
Cc:     Trond Myklebust <trondmy@...marydata.com>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>
Subject: Re: [GIT PULL] Please pull NFS client fixes for 4.12

On Thu 11-05-17 10:53:27, Nikolay Borisov wrote:
> 
> 
> On 10.05.2017 19:47, Trond Myklebust wrote:
[...]
> > - Cleanup and removal of some memory failure paths now that
> >   GFP_NOFS is guaranteed to never fail.
> 
> What guarantees that? Since if this is the case then this can result in
> a lot of opportunities for cleanup across the whole kernel tree. After
> discussing with mhocko (cc'ed) it seems that in practice everything
> below COSTLY_ORDER which are not GFP_NORETRY will never fail. But this
> semantic is not the same as GFP_NOFAIL. E.g. nothing guarantees that
> this will stay like that in the future?

In practice it is hard to change the semantic of small allocations never
fail _practically_. But this is absolutely not guaranteed! They can fail
e.g. when the allocation context is the oom victim. Removing error paths
for allocation failures is just wrong.
-- 
Michal Hocko
SUSE Labs