From: Cupertino Miranda <cupertino.miranda@oracle.com>
To: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>
Cc: libc-alpha@sourceware.org
Subject: Re: [PATCH v3 1/1] Created tunable to force small pages on stack allocation.
Date: Tue, 28 Mar 2023 09:48:51 +0100 [thread overview]
Message-ID: <87edp9i7m4.fsf@oracle.com> (raw)
In-Reply-To: <8d44ed82-72c3-9ff4-47d1-8822ec9225c9@linaro.org>
Adhemerval Zanella Netto via Libc-alpha writes:
> On 21/03/23 11:51, Cupertino Miranda via Libc-alpha wrote:
>> Created tunable glibc.pthread.stack_hugetlb to control when hugepages
>> can be used for stack allocation.
>> In case THP are enabled and glibc.pthread.stack_hugetlb is set to
>> 0, glibc will madvise the kernel not to use allow hugepages for stack
>> allocations.
>>
>> Changed from v1:
>> - removed the __malloc_thp_mode calls to check if hugetlb is
>> enabled.
>>
>> Changed from v2:
>> - Added entry in manual/tunables.texi
>> - Fixed tunable default to description
>> - Code style corrections.
>> ---
>> manual/tunables.texi | 11 +++++++++++
>> nptl/allocatestack.c | 6 ++++++
>> nptl/nptl-stack.c | 1 +
>> nptl/nptl-stack.h | 3 +++
>> nptl/pthread_mutex_conf.c | 8 ++++++++
>> sysdeps/nptl/dl-tunables.list | 6 ++++++
>> 6 files changed, 35 insertions(+)
>>
>> diff --git a/manual/tunables.texi b/manual/tunables.texi
>> index 70dd2264c5..de6fd9d6b3 100644
>> --- a/manual/tunables.texi
>> +++ b/manual/tunables.texi
>> @@ -459,6 +459,17 @@ registration on behalf of the application.
>> Restartable sequences are a Linux-specific extension.
>> @end deftp
>>
>> +@deftp Tunable glibc.pthread.stack_hugetlb
>> +This tunable allows to configure stack allocation never to use hugetlbs.
>
> I think we should improve the wording here to make it clear this for the
> stack allocated for newly created threads even though the tunables
> name implies it ('stack allocation' might infer that all stack allocation,
> even for single-thread programs) and that does not affect stack set by
> pthread_attr_setstack.
Thanks for the feedback. Will update it right away.
>
>> +This is more of an RSS optimization, for example in scenarios where many
>> +threads get created, keeping RSS to a minimum, but also allowing hugestlbs to
>> +be used for malloc allocations.
>> +
>> +The default is @samp{1} and preservs glibc default behaviour.
>> +When set to @samp{0}, it advises the kernel not to use hugetlbs for stack
>> +allocation.
>> +@end deftp
>> +
>> @node Hardware Capability Tunables
>> @section Hardware Capability Tunables
>> @cindex hardware capability tunables
>> diff --git a/nptl/allocatestack.c b/nptl/allocatestack.c
>> index c7adbccd6f..f9d8cdfd08 100644
>> --- a/nptl/allocatestack.c
>> +++ b/nptl/allocatestack.c
>> @@ -369,6 +369,12 @@ allocate_stack (const struct pthread_attr *attr, struct pthread **pdp,
>> if (__glibc_unlikely (mem == MAP_FAILED))
>> return errno;
>>
>> + /* Do madvise in case the tunable glibc.pthread.stack_hugetlb is
>> + set to 0, disabling hugetlb. */
>> + if (__glibc_unlikely (__nptl_stack_hugetlb == 0)
>> + && __madvise (mem, size, MADV_NOHUGEPAGE) != 0)
>> + return errno;
>> +
>> /* SIZE is guaranteed to be greater than zero.
>> So we can never get a null pointer back from mmap. */
>> assert (mem != NULL);
>> diff --git a/nptl/nptl-stack.c b/nptl/nptl-stack.c
>> index 5eb7773575..e829711cb5 100644
>> --- a/nptl/nptl-stack.c
>> +++ b/nptl/nptl-stack.c
>> @@ -21,6 +21,7 @@
>> #include <pthreadP.h>
>>
>> size_t __nptl_stack_cache_maxsize = 40 * 1024 * 1024;
>> +int32_t __nptl_stack_hugetlb = 1;
>>
>> void
>> __nptl_stack_list_del (list_t *elem)
>> diff --git a/nptl/nptl-stack.h b/nptl/nptl-stack.h
>> index 34f8bbb15e..cf90b27c2b 100644
>> --- a/nptl/nptl-stack.h
>> +++ b/nptl/nptl-stack.h
>> @@ -27,6 +27,9 @@
>> /* Maximum size of the cache, in bytes. 40 MiB by default. */
>> extern size_t __nptl_stack_cache_maxsize attribute_hidden;
>>
>> +/* Should allow stacks to use hugetlb. (1) is default. */
>> +extern int32_t __nptl_stack_hugetlb;
>> +
>> /* Check whether the stack is still used or not. */
>> static inline bool
>> __nptl_stack_in_use (struct pthread *pd)
>> diff --git a/nptl/pthread_mutex_conf.c b/nptl/pthread_mutex_conf.c
>> index 329c4cbb8f..60ef9095aa 100644
>> --- a/nptl/pthread_mutex_conf.c
>> +++ b/nptl/pthread_mutex_conf.c
>> @@ -45,6 +45,12 @@ TUNABLE_CALLBACK (set_stack_cache_size) (tunable_val_t *valp)
>> __nptl_stack_cache_maxsize = valp->numval;
>> }
>>
>> +static void
>> +TUNABLE_CALLBACK (set_stack_hugetlb) (tunable_val_t *valp)
>> +{
>> + __nptl_stack_hugetlb = (int32_t) valp->numval;
>> +}
>> +
>> void
>> __pthread_tunables_init (void)
>> {
>> @@ -52,5 +58,7 @@ __pthread_tunables_init (void)
>> TUNABLE_CALLBACK (set_mutex_spin_count));
>> TUNABLE_GET (stack_cache_size, size_t,
>> TUNABLE_CALLBACK (set_stack_cache_size));
>> + TUNABLE_GET (stack_hugetlb, int32_t,
>> + TUNABLE_CALLBACK (set_stack_hugetlb));
>> }
>> #endif
>> diff --git a/sysdeps/nptl/dl-tunables.list b/sysdeps/nptl/dl-tunables.list
>> index bd1ddb121d..4cde9500b6 100644
>> --- a/sysdeps/nptl/dl-tunables.list
>> +++ b/sysdeps/nptl/dl-tunables.list
>> @@ -33,5 +33,11 @@ glibc {
>> maxval: 1
>> default: 1
>> }
>> + stack_hugetlb {
>> + type: INT_32
>> + minval: 0
>> + maxval: 1
>> + default: 1
>> + }
>> }
>> }
prev parent reply other threads:[~2023-03-28 8:49 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-21 14:51 [PATCH v3 0/1] *** " Cupertino Miranda
2023-03-21 14:51 ` [PATCH v3 1/1] " Cupertino Miranda
2023-03-27 20:26 ` Adhemerval Zanella Netto
2023-03-28 8:48 ` Cupertino Miranda [this message]
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