Date: Thu, 9 Feb 2017 22:36:56 +0900 From: Hoeun Ryu <hoeun.ryu@...il.com> To: Michal Hocko <mhocko@...nel.org> Cc: Kees Cook <keescook@...omium.org>, Michal Marek <mmarek@...e.com>, Andrew Morton <akpm@...ux-foundation.org>, Emese Revfy <re.emese@...il.com>, Ingo Molnar <mingo@...nel.org>, Mickaël Salaün <mic@...ikod.net>, Nicholas Piggin <npiggin@...il.com>, Andy Lutomirski <luto@...nel.org>, "Eric W. Biederman" <ebiederm@...ssion.com>, Mateusz Guzik <mguzik@...hat.com>, linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com Subject: Re: [PATCH v2 2/2] fork: make number of cached stacks (vmapped) configurable using Kbuild On Thu, Feb 9, 2017 at 5:40 PM, Michal Hocko <mhocko@...nel.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@...il.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
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