linux-kernel - Re: [PATCH 1/4] mm/vmalloc: allow to call vfree() in atomic context

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <d28bc808-0aab-d36a-f401-9925680fd131@virtuozzo.com>
Date:   Wed, 5 Apr 2017 13:31:23 +0300
From:   Andrey Ryabinin <aryabinin@...tuozzo.com>
To:     Michal Hocko <mhocko@...nel.org>
CC:     Thomas Hellstrom <thellstrom@...are.com>,
        <akpm@...ux-foundation.org>, <penguin-kernel@...ove.SAKURA.ne.jp>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        <hpa@...or.com>, <chris@...is-wilson.co.uk>, <hch@....de>,
        <mingo@...e.hu>, <jszhang@...vell.com>, <joelaf@...gle.com>,
        <joaodias@...gle.com>, <willy@...radead.org>, <tglx@...utronix.de>,
        <stable@...r.kernel.org>
Subject: Re: [PATCH 1/4] mm/vmalloc: allow to call vfree() in atomic context

On 04/04/2017 12:41 PM, Michal Hocko wrote:
> On Thu 30-03-17 17:48:39, Andrey Ryabinin wrote:
>> From: Andrey Ryabinin <aryabinin@...tuozzo.com>
>> Subject: mm/vmalloc: allow to call vfree() in atomic context fix
>>
>> Don't spawn worker if we already purging.
>>
>> Signed-off-by: Andrey Ryabinin <aryabinin@...tuozzo.com>
> 
> I would rather put this into a separate patch. Ideally with some numners
> as this is an optimization...
> 

It's quite simple optimization and don't think that this deserves to be a separate patch.

But I did some measurements though. With enabled VMAP_STACK=y and NR_CACHED_STACK changed to 0
running fork() 100000 times gives this:

With optimization:

~ # grep try_purge /proc/kallsyms 
ffffffff811d0dd0 t try_purge_vmap_area_lazy
~ # perf stat --repeat 10 -ae workqueue:workqueue_queue_work --filter 'function == 0xffffffff811d0dd0' ./fork

 Performance counter stats for 'system wide' (10 runs):

                15      workqueue:workqueue_queue_work                                     ( +-  0.88% )

       1.615368474 seconds time elapsed                                          ( +-  0.41% )


Without optimization:
~ # grep try_purge /proc/kallsyms 
ffffffff811d0dd0 t try_purge_vmap_area_lazy
~ # perf stat --repeat 10 -ae workqueue:workqueue_queue_work --filter 'function == 0xffffffff811d0dd0' ./fork

 Performance counter stats for 'system wide' (10 runs):

                30      workqueue:workqueue_queue_work                                     ( +-  1.31% )

       1.613231060 seconds time elapsed                                          ( +-  0.38% )


So there is no measurable difference on the test itself, but we queue twice more jobs without this optimization.
It should decrease load of kworkers.



>> ---
>>  mm/vmalloc.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
>> index ea1b4ab..88168b8 100644
>> --- a/mm/vmalloc.c
>> +++ b/mm/vmalloc.c
>> @@ -737,7 +737,8 @@ static void free_vmap_area_noflush(struct vmap_area *va)
>>  	/* After this point, we may free va at any time */
>>  	llist_add(&va->purge_list, &vmap_purge_list);
>>  
>> -	if (unlikely(nr_lazy > lazy_max_pages()))
>> +	if (unlikely(nr_lazy > lazy_max_pages()) &&
>> +	    !mutex_is_locked(&vmap_purge_lock))
>>  		schedule_work(&purge_vmap_work);
>>  }
>>  
>> -- 
>> 2.10.2
>>
>