Date: Thu, 9 Feb 2017 09:40:06 +0100 From: Michal Hocko <mhocko@...nel.org> To: Hoeun Ryu <hoeun.ryu@...il.com> 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 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. > 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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