linux-kernel - Re: [PATCH 1/6] mm: introduce kv[mz]alloc helpers

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Date:   Mon, 16 Jan 2017 20:40:53 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        David Rientjes <rientjes@...gle.com>,
        Mel Gorman <mgorman@...e.de>,
        Johannes Weiner <hannes@...xchg.org>,
        Al Viro <viro@...iv.linux.org.uk>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>,
        Anatoly Stepanov <astepanov@...udlinux.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Theodore Ts'o <tytso@....edu>
Subject: Re: [PATCH 1/6] mm: introduce kv[mz]alloc helpers

On Mon 16-01-17 11:09:37, John Hubbard wrote:
> 
> 
> On 01/16/2017 12:47 AM, Michal Hocko wrote:
> > On Sun 15-01-17 20:34:13, John Hubbard wrote:
[...]
> > > Is that "Reclaim modifiers" line still true, or is it a leftover from an
> > > earlier approach? I am having trouble reconciling it with rest of the
> > > patchset, because:
> > > 
> > > a) the flags argument below is effectively passed on to either kmalloc_node
> > > (possibly adding, but not removing flags), or to __vmalloc_node_flags.
> > 
> > The above only says thos are _unsupported_ - in other words the behavior
> > is not defined. Even if flags are passed down to kmalloc resp. vmalloc
> > it doesn't mean they are used that way.  Remember that vmalloc uses
> > some hardcoded GFP_KERNEL allocations.  So while I could be really
> > strict about this and mask away these flags I doubt this is worth the
> > additional code.
> 
> I do wonder about passing those flags through to kmalloc. Maybe it is worth
> stripping out __GFP_NORETRY and __GFP_NOFAIL, after all. It provides some
> insulation from any future changes to the implementation of kmalloc, and it
> also makes the documentation more believable.

I am not really convinced that we should take an extra steps for these
flags. There are no existing users for those flags and new users should
follow the documentation.

-- 
Michal Hocko
SUSE Labs