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

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Message-ID: <CAAmzW4M2EDFX7XsK7kgwEaGgZBBnVb97rGHwinaNLt8Q==TP1w@mail.gmail.com>
Date:	Wed, 18 Mar 2015 14:07:17 +0900
From:	Joonsoo Kim <js1304@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Roman Peniaev <r.peniaev@...il.com>,
	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 Memory Management List <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

2015-03-18 6:58 GMT+09:00 Andrew Morton <akpm@...ux-foundation.org>:
> 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

I misunderstand before and my scenario isn't possible. So, I'm fine with
current patch.

Thanks.
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