linux-kernel - Re: [PATCH V2 2/2] mm/memblock.c: check return value of memblock_reserve() in memblock_virt_alloc

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Message-ID: <20161221132200.GK31118@dhcp22.suse.cz>
Date:   Wed, 21 Dec 2016 14:22:01 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Wei Yang <richard.weiyang@...il.com>
Cc:     trivial@...nel.org, akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 2/2] mm/memblock.c: check return value of
 memblock_reserve() in memblock_virt_alloc_internal()

On Wed 21-12-16 13:13:32, Wei Yang wrote:
> On Wed, Dec 21, 2016 at 08:51:16AM +0100, Michal Hocko wrote:
> >On Tue 20-12-16 16:48:23, Wei Yang wrote:
> >> On Mon, Dec 19, 2016 at 04:21:57PM +0100, Michal Hocko wrote:
> >> >On Sun 18-12-16 14:47:50, Wei Yang wrote:
> >> >> memblock_reserve() may fail in case there is not enough regions.
> >> >
> >> >Have you seen this happenning in the real setups or this is a by-review
> >> >driven change?
> >> 
> >> This is a by-review driven change.
> >> 
> >> >[...]
> >> >>  again:
> >> >>  	alloc = memblock_find_in_range_node(size, align, min_addr, max_addr,
> >> >>  					    nid, flags);
> >> >> -	if (alloc)
> >> >> +	if (alloc && !memblock_reserve(alloc, size))
> >> >>  		goto done;
> >
> >So how exactly does the reserve fail when memblock_find_in_range_node
> >found a suitable range for the given size?
> >
> 
> Even memblock_find_in_range_node() gets a suitable range, memblock_reserve()
> still could fail. And the case just happens when memblock can't resize.
> memblock_reserve() reserve a range by adding a range to memblock.reserved. In
> case the memblock.reserved is full and can't resize, this fails.

Sorry for being dense but what does it mean that the reserved will get
full? Also how probable is such a situation? Is it even real? In other
words does this fix a real or only a theoretical problem?

Anyway this all should be part of the changelog.
-- 
Michal Hocko
SUSE Labs