Re: [PATCH 1/3] mm/vmalloc: fix possible exhaustion of vmalloc space caused by vm_map_ram allocator

[Joonsoo Kim <js1304@gmail.com>]

2015-03-18 6:58 GMT+09:00 Andrew Morton <akpm@linux-foundation.org>:
> On Tue, 17 Mar 2015 17:22:46 +0900 Roman Peniaev <r.peniaev@gmail.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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