linux-kernel - Re: [PATCH 1/2] mm/vmap: Add a notifier for when we run out of vmap address space

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Date:	Thu, 17 Mar 2016 12:57:36 +0000
From:	Chris Wilson <chris@...is-wilson.co.uk>
To:	Roman Peniaev <r.peniaev@...il.com>
Cc:	intel-gfx@...ts.freedesktop.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	Mel Gorman <mgorman@...hsingularity.net>, linux-mm@...ck.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] mm/vmap: Add a notifier for when we run out of vmap
 address space

On Thu, Mar 17, 2016 at 01:37:06PM +0100, Roman Peniaev wrote:
> > +       freed = 0;
> > +       blocking_notifier_call_chain(&vmap_notify_list, 0, &freed);
> 
> It seems to me that alloc_vmap_area() was designed not to sleep,
> at least on GFP_NOWAIT path (__GFP_DIRECT_RECLAIM is not set).
> 
> But blocking_notifier_call_chain() might sleep.

Indeed, I had not anticipated anybody using GFP_ATOMIC or equivalently
restrictive gfp_t for vmap and yes there are such callers.

Would guarding the notifier with gfp & __GFP_DIRECT_RECLAIM and
!(gfp & __GFP_NORETRY) == be sufficient? Is that enough for GFP_NOFS?
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre