linux-kernel - Re: [PATCH 1/3] mm/vmalloc: fix possible exhaustion of vmalloc space caused by vm_map

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Message-Id: <20150317145823.3213cba4dc629c716df0fdd9@linux-foundation.org>
Date:	Tue, 17 Mar 2015 14:58:23 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Roman Peniaev <r.peniaev@...il.com>
Cc:	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Eric Dumazet <edumazet@...gle.com>,
	David Rientjes <rientjes@...gle.com>,
	WANG Chao <chaowang@...hat.com>,
	Fabian Frederick <fabf@...net.be>,
	Christoph Lameter <cl@...ux.com>, Gioh Kim <gioh.kim@....com>,
	Rob Jones <rob.jones@...ethink.co.uk>, linux-mm@...ck.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH 1/3] mm/vmalloc: fix possible exhaustion of vmalloc
 space caused by vm_map_ram allocator

On Tue, 17 Mar 2015 17:22:46 +0900 Roman Peniaev <r.peniaev@...il.com> wrote:

> >> My second patch fixes this problem.
> >> I occupy the block on allocation and avoid jumping to the search loop.
> >
> > I'm not sure that this fixes above case.
> > 'vm_map_ram (3) * 85' means 85 times vm_map_ram() calls.
> >
> > First vm_map_ram(3) caller could get benefit from your second patch.
> > But, second caller and the other callers in each iteration could not
> > get benefit and should iterate whole list to find suitable free block,
> > because this free block is put to the tail of the list. Am I missing
> > something?
> 
> You are missing the fact that we occupy blocks in 2^n.
> So in your example 4 page slots will be occupied (order is 2), not 3.

Could you please

- update the changelogs so they answer the questions which Joonsoo
  Kim and Gioh Kim asked

- write a little in-kernel benchmark to test the scenario which
  Joonsoo described and include the before and after timing results in
  the changelogs

- resend the patchset

Thanks.
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