Messages in this thread | | | Date | Thu, 9 Feb 2017 09:40:06 +0100 | From | Michal Hocko <> | Subject | Re: [PATCH v2 2/2] fork: make number of cached stacks (vmapped) configurable using Kbuild |
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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@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
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