| Message ID | 1486613040-30555-2-git-send-email-hoeun.ryu@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, Feb 09, 2017 at 01:03:47PM +0900, Hoeun Ryu wrote: > +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. > + Can you explain in the help text under what circumstances someone should change this, and to what value? As-is, it seems like somewhat of a useless config option which no one will ever change. - Eric
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 >
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
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
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. Signed-off-by: Hoeun Ryu <hoeun.ryu@gmail.com> --- arch/Kconfig | 8 ++++++++ kernel/fork.c | 2 +- 2 files changed, 9 insertions(+), 1 deletion(-)