From: Hoeun Ryu <hoeun.ryu@gmail.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: "Kees Cook" <keescook@chromium.org>,
"Michal Marek" <mmarek@suse.com>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Emese Revfy" <re.emese@gmail.com>,
"Ingo Molnar" <mingo@kernel.org>,
"Mickaël Salaün" <mic@digikod.net>,
"Nicholas Piggin" <npiggin@gmail.com>,
"Andy Lutomirski" <luto@kernel.org>,
"Eric W. Biederman" <ebiederm@xmission.com>,
"Mateusz Guzik" <mguzik@redhat.com>,
linux-kernel@vger.kernel.org,
kernel-hardening@lists.openwall.com
Subject: Re: [PATCH v2 2/2] fork: make number of cached stacks (vmapped) configurable using Kbuild
Date: Thu, 9 Feb 2017 22:36:56 +0900 [thread overview]
Message-ID: <CABeRdto3viSm7EZbWOCXkxdsjpp-ahpAaL3G3ZRaEVBN5hXc8A@mail.gmail.com> (raw)
In-Reply-To: <20170209084005.GC10257@dhcp22.suse.cz>
On Thu, Feb 9, 2017 at 5:40 PM, Michal Hocko <mhocko@kernel.org> wrote:
> On Thu 09-02-17 13:03:47, Hoeun Ryu wrote:
>> Introducing NR_VMAP_STACK_CACHE, the number of cached stacks for virtually
>> mapped kernel stack can be configurable using Kbuild system.
>> default value is 2.
>
> This should really explain _why_ we want/need this. The config space is
> really large already and there should better be a good reason to make it
> even larger. Which workload will benefit from a different than default
> cache size and why?
>
> Without a really good reasons NACK from me.
>
OK, I understand your NACK. Thank you.
>> Signed-off-by: Hoeun Ryu <hoeun.ryu@gmail.com>
>> ---
>> arch/Kconfig | 8 ++++++++
>> kernel/fork.c | 2 +-
>> 2 files changed, 9 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/Kconfig b/arch/Kconfig
>> index d49a8e6..066d111 100644
>> --- a/arch/Kconfig
>> +++ b/arch/Kconfig
>> @@ -849,6 +849,14 @@ config VMAP_STACK
>> the stack to map directly to the KASAN shadow map using a formula
>> that is incorrect if the stack is in vmalloc space.
>>
>> +config NR_VMAP_STACK_CACHE
>> + int "Number of cached stacks"
>> + default "2"
>> + depends on VMAP_STACK
>> + help
>> + This determines how many stacks can be cached for virtually
>> + mapped kernel stacks.
>> +
>> config ARCH_WANT_RELAX_ORDER
>> bool
>>
>> diff --git a/kernel/fork.c b/kernel/fork.c
>> index 7911ed2..73ba1da 100644
>> --- a/kernel/fork.c
>> +++ b/kernel/fork.c
>> @@ -166,7 +166,7 @@ void __weak arch_release_thread_stack(unsigned long *stack)
>> * vmalloc() is a bit slow, and calling vfree() enough times will force a TLB
>> * flush. Try to minimize the number of calls by caching stacks.
>> */
>> -#define NR_CACHED_STACKS 2
>> +#define NR_CACHED_STACKS CONFIG_NR_VMAP_STACK_CACHE
>> static DEFINE_PER_CPU(struct vm_struct *, cached_stacks[NR_CACHED_STACKS]);
>> #endif
>>
>> --
>> 2.7.4
>>
>
> --
> Michal Hocko
> SUSE Labs
next prev parent reply other threads:[~2017-02-09 13:37 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-09 4:03 [PATCH v2 1/2] fork: free vmapped stacks in cache when cpus are offline Hoeun Ryu
2017-02-09 4:03 ` [PATCH v2 2/2] fork: make number of cached stacks (vmapped) configurable using Kbuild Hoeun Ryu
2017-02-09 4:26 ` [kernel-hardening] " Eric Biggers
2017-02-09 8:40 ` Michal Hocko
2017-02-09 13:36 ` Hoeun Ryu [this message]
2017-02-09 4:22 ` [kernel-hardening] [PATCH v2 1/2] fork: free vmapped stacks in cache when cpus are offline Eric Biggers
2017-02-09 13:35 ` Hoeun Ryu
2017-02-09 7:28 ` kbuild test robot
2017-02-09 8:01 ` kbuild test robot
2017-02-09 8:38 ` Michal Hocko
2017-02-09 13:36 ` Hoeun Ryu
2017-02-09 10:26 ` kbuild test robot
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