From: Andy Lutomirski <luto@kernel.org>
To: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Dave Hansen <dave.hansen@intel.com>,
LKML <linux-kernel@vger.kernel.org>,
Christoph Hellwig <hch@infradead.org>,
Linux-MM <linux-mm@kvack.org>, Andy Lutomirski <luto@kernel.org>
Subject: Re: [PATCH 3/4] kernel/fork: switch vmapped stack callation to __vmalloc_area()
Date: Wed, 21 Feb 2018 16:35:37 +0000 [thread overview]
Message-ID: <CALCETrXU5rq4HHvp2y0GZrvt85hRO=PEMakUQ938+mxF2xYwzw@mail.gmail.com> (raw)
In-Reply-To: <d636d1cb-88d9-8474-d5bc-fb2994108919@yandex-team.ru>
On Wed, Feb 21, 2018 at 7:23 AM, Konstantin Khlebnikov
<khlebnikov@yandex-team.ru> wrote:
>
>
> On 21.02.2018 03:16, Andrew Morton wrote:
>>
>> On Tue, 23 Jan 2018 16:57:21 +0300 Konstantin Khlebnikov
>> <khlebnikov@yandex-team.ru> wrote:
>>
>>> # stress-ng --clone 100 -t 10s --metrics-brief
>>> at 32-core machine shows boost 35000 -> 36000 bogo ops
>>>
>>> Patch 4/4 is a kind of RFC.
>>> Actually per-cpu cache of preallocated stacks works faster than buddy
>>> allocator thus
>>> performance boots for it happens only at completely insane rate of
>>> clones.
>>>
>>
>> I'm not really sure what to make of this patchset. Is it useful in any
>> known real-world use cases?
>
>
> Not yet. Feel free to ignore last patch.
>
>>
>>> + This option neutralize stack overflow protection but allows to
>>> + achieve best performance for syscalls fork() and clone().
>>
>>
>> That sounds problematic, but perhaps acceptable if the fallback only
>> happens rarely.
>>
>> Can this code be folded into CONFIG_VMAP_STACk in some cleaner fashion?
>> We now have options for non-vmapped stacks, vmapped stacks and a mix
>> of both.
>>
>> And what about this comment in arch/Kconfig:VMAP_STACK:
>>
>> This is presently incompatible with KASAN because KASAN expects
>> the stack to map directly to the KASAN shadow map using a
>> formula
>> that is incorrect if the stack is in vmalloc space.
>>
>>
>> So VMAP_STACK_AS_FALLBACK will intermittently break KASAN?
>>
>
> All of this (including CONFIG_VMAP_STACK) could be turned into boot option.
> I think this would be a best solution.
Or someone could *fix* KASAN to work with stacks in the vmalloc area.
next prev parent reply other threads:[~2018-02-21 16:36 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-23 10:55 [PATCH 1/4] vmalloc: add vm_flags argument to internal __vmalloc_node() Konstantin Khlebnikov
2018-01-23 10:55 ` [PATCH 2/4] vmalloc: add __vmalloc_area() Konstantin Khlebnikov
2018-01-23 10:55 ` [PATCH 3/4] kernel/fork: switch vmapped stack callation to __vmalloc_area() Konstantin Khlebnikov
2018-01-23 13:57 ` Konstantin Khlebnikov
2018-02-21 0:16 ` Andrew Morton
2018-02-21 7:23 ` Konstantin Khlebnikov
2018-02-21 16:35 ` Andy Lutomirski [this message]
2018-01-23 10:55 ` [PATCH 4/4] kernel/fork: add option to use virtually mapped stacks as fallback Konstantin Khlebnikov
2018-02-21 15:42 ` Use higher-order pages in vmalloc Matthew Wilcox
2018-02-21 16:11 ` Andy Lutomirski
2018-02-21 16:50 ` Matthew Wilcox
2018-02-21 16:16 ` Dave Hansen
2018-02-21 17:01 ` Matthew Wilcox
2018-02-22 6:59 ` Michal Hocko
2018-02-22 12:22 ` Matthew Wilcox
2018-02-22 13:36 ` Michal Hocko
2018-02-22 19:01 ` Andy Lutomirski
2018-02-22 19:19 ` Dave Hansen
2018-02-22 19:27 ` Andy Lutomirski
2018-02-22 19:36 ` Dave Hansen
2018-02-23 12:13 ` Michal Hocko
2018-03-01 18:16 ` Eric Dumazet
2018-02-21 12:24 ` [PATCH 1/4] vmalloc: add vm_flags argument to internal __vmalloc_node() Matthew Wilcox
2018-02-21 12:39 ` Andrey Ryabinin
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