linux-kernel - Re: [PATCH] mm: support __GFP_REPEAT in kvmalloc

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Date:   Fri, 6 Jan 2017 13:31:17 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        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>, kvm@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-security-module@...r.kernel.org, linux-ext4@...r.kernel.org,
        Joe Perches <joe@...ches.com>,
        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>,
        Andreas Dilger <adilger@...ger.ca>
Subject: Re: [PATCH] mm: support __GFP_REPEAT in kvmalloc_node

On Fri 06-01-17 13:09:36, Vlastimil Babka wrote:
> On 01/04/2017 07:12 PM, Michal Hocko wrote:
[...]
> > diff --git a/mm/util.c b/mm/util.c
> > index 8e4ea6cbe379..a2bfb85e60e5 100644
> > --- a/mm/util.c
> > +++ b/mm/util.c
> > @@ -348,8 +348,13 @@ void *kvmalloc_node(size_t size, gfp_t flags, int node)
> >  	 * Make sure that larger requests are not too disruptive - no OOM
> >  	 * killer and no allocation failure warnings as we have a fallback
> >  	 */
> > -	if (size > PAGE_SIZE)
> > -		kmalloc_flags |= __GFP_NORETRY | __GFP_NOWARN;
> > +	if (size > PAGE_SIZE) {
> > +		kmalloc_flags |= __GFP_NOWARN;
> > +
> > +		if (!(kmalloc_flags & __GFP_REPEAT) ||
> > +				(size <= PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER))
> > +			kmalloc_flags |= __GFP_NORETRY;
> 
> I think this would be more understandable for me if it was written in
> the opposite way, i.e. "if we have costly __GFP_REPEAT allocation, don't
> use __GFP_NORETRY",

Dunno, doesn't look much simpler to me
		kmalloc_flags |= __GFP_NORETRY;
		if ((kmalloc_flags & __GFP_REPEAT) &&
				(size > PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER)) {
			kmalloc_flags &= ~__GFP_NORETRY;
		}

> but nevermind, seems correct to me wrt current
> handling of both flags in the page allocator. And it serves as a good
> argument to have this wrapper in mm/ as we are hopefully more likely to
> keep it working as intended with future changes, than all the opencoded
> variants.
> 
> Acked-by: Vlastimil Babka <vbabka@...e.cz>

Thanks!

-- 
Michal Hocko
SUSE Labs