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From: Roman Peniaev <r.peniaev@gmail.com>
To: Gioh Kim <gioh.kim@lge.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Eric Dumazet <edumazet@google.com>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	David Rientjes <rientjes@google.com>,
	WANG Chao <chaowang@redhat.com>,
	Fabian Frederick <fabf@skynet.be>,
	Christoph Lameter <cl@linux.com>,
	Rob Jones <rob.jones@codethink.co.uk>,
	linux-mm@kvack.org,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: Re: [PATCH 0/3] [RFC] mm/vmalloc: fix possible exhaustion of vmalloc space
Date: Mon, 16 Mar 2015 19:57:32 +0900	[thread overview]
Message-ID: <CACZ9PQVV6QoRBVoCJL8XZRBAAhSJvRg=jtkmWRgSELzeywZPdw@mail.gmail.com> (raw)
In-Reply-To: <CACZ9PQXe6C1Cpt+zGD7ew2AXgcA2pD047BrXz9GXfz2ZhKuCAQ@mail.gmail.com>

On Mon, Mar 16, 2015 at 7:49 PM, Roman Peniaev <r.peniaev@gmail.com> wrote:
> On Mon, Mar 16, 2015 at 7:28 PM, Gioh Kim <gioh.kim@lge.com> wrote:
>>
>>
>> 2015-03-13 오후 9:12에 Roman Pen 이(가) 쓴 글:
>>> Hello all.
>>>
>>> Recently I came across high fragmentation of vm_map_ram allocator: vmap_block
>>> has free space, but still new blocks continue to appear.  Further investigation
>>> showed that certain mapping/unmapping sequence can exhaust vmalloc space.  On
>>> small 32bit systems that's not a big problem, cause purging will be called soon
>>> on a first allocation failure (alloc_vmap_area), but on 64bit machines, e.g.
>>> x86_64 has 45 bits of vmalloc space, that can be a disaster.
>>
>> I think the problem you comments is already known so that I wrote comments about it as
>> "it could consume lots of address space through fragmentation".
>>
>> Could you tell me about your situation and reason why it should be avoided?
>
> In the first patch of this set I explicitly described the function,
> which exhausts
> vmalloc space without any chance to be purged: vm_map_ram allocator is
> greedy and firstly
> tries to occupy newly allocated block, even old blocks contain enough
> free space.
>
> This can be easily fixed if we put newly allocated block (which has
> enough space to
> complete further requests) to the tail of a free list, to give a
> chance to old blocks.
>
> Why it should be avoided?  Strange question.  For me it looks like a
> bug of an allocator,
> which should be fair and should not continuously allocate new blocks
> without lazy purging
> (seems vmap_lazy_nr and  __purge_vmap_area_lazy were created exactly
> for those reasons:
>  to avoid infinite allocations)


And if you are talking about your commit 364376383, which adds this comment

 * If you use this function for less than VMAP_MAX_ALLOC pages, it could be
 * faster than vmap so it's good.  But if you mix long-life and short-life
 * objects with vm_map_ram(), it could consume lots of address space through
 * fragmentation (especially on a 32bit machine).  You could see failures in
 * the end.  Please use this function for short-lived objects.

This is not that case, because if block is pinned, i.e. some pages are still
in use, we can't do anything with that.

I am talking about blocks, which are completely freed, but dirty.


--
Roman

>
>
> --
> Roman
>
>
>>
>>
>>>
>>> Fixing this I also did some tweaks in allocation logic of a new vmap block and
>>> replaced dirty bitmap with min/max dirty range values to make the logic simpler.
>>>
>>> I would like to receive comments on the following three patches.
>>>
>>> Thanks.
>>>
>>> Roman Pen (3):
>>>    mm/vmalloc: fix possible exhaustion of vmalloc space caused by
>>>      vm_map_ram allocator
>>>    mm/vmalloc: occupy newly allocated vmap block just after allocation
>>>    mm/vmalloc: get rid of dirty bitmap inside vmap_block structure
>>>
>>>   mm/vmalloc.c | 94 ++++++++++++++++++++++++++++++++++--------------------------
>>>   1 file changed, 54 insertions(+), 40 deletions(-)
>>>
>>> Cc: Andrew Morton <akpm@linux-foundation.org>
>>> Cc: Nick Piggin <npiggin@kernel.dk>
>>> Cc: Eric Dumazet <edumazet@google.com>
>>> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
>>> Cc: David Rientjes <rientjes@google.com>
>>> Cc: WANG Chao <chaowang@redhat.com>
>>> Cc: Fabian Frederick <fabf@skynet.be>
>>> Cc: Christoph Lameter <cl@linux.com>
>>> Cc: Gioh Kim <gioh.kim@lge.com>
>>> Cc: Rob Jones <rob.jones@codethink.co.uk>
>>> Cc: linux-mm@kvack.org
>>> Cc: linux-kernel@vger.kernel.org
>>> Cc: stable@vger.kernel.org
>>>

      reply	other threads:[~2015-03-16 10:57 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-13 12:12 Roman Pen
2015-03-13 12:12 ` [PATCH 1/3] mm/vmalloc: fix possible exhaustion of vmalloc space caused by vm_map_ram allocator Roman Pen
2015-03-17  4:56   ` Joonsoo Kim
2015-03-17  5:12     ` Roman Peniaev
2015-03-17  7:29       ` Joonsoo Kim
2015-03-17  8:22         ` Roman Peniaev
2015-03-17 21:58           ` Andrew Morton
2015-03-18  5:07             ` Joonsoo Kim
2015-03-18  5:05           ` Joonsoo Kim
2015-03-13 12:12 ` [PATCH 2/3] mm/vmalloc: occupy newly allocated vmap block just after allocation Roman Pen
2015-03-18  5:51   ` Joonsoo Kim
2015-03-13 12:12 ` [PATCH 3/3] mm/vmalloc: get rid of dirty bitmap inside vmap_block structure Roman Pen
2015-03-18  5:52   ` Joonsoo Kim
2015-03-16 10:28 ` [PATCH 0/3] [RFC] mm/vmalloc: fix possible exhaustion of vmalloc space Gioh Kim
2015-03-16 10:49   ` Roman Peniaev
2015-03-16 10:57     ` Roman Peniaev [this message]

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