[PATCH v6 0/1] *** Created tunable to force small pages on stack allocation.

[PATCH v6 0/1] *** Created tunable to force small pages on stack allocation.

[Cupertino Miranda]

Hi,

This is a correction to previous that failed to apply in
patchwork.

Regards,
Cupertino

Cupertino Miranda (1):
  Created tunable to force small pages on stack allocation.

 NEWS                          |  3 +++
 manual/tunables.texi          | 15 +++++++++++++++
 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 ++++++
 7 files changed, 42 insertions(+)

-- 
2.38.1

[PATCH v6 1/1] Created tunable to force small pages on stack allocation.

[Cupertino Miranda]

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.

Changes from v3:
 - Improve tunables.texi.

Changes from v4:
 - Improved text in tunables.texi by suggestion of Adhemerval.

Changes from v5:
 - Added a new entry in NEWS.
---
 NEWS                          |  3 +++
 manual/tunables.texi          | 15 +++++++++++++++
 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 ++++++
 7 files changed, 42 insertions(+)

diff --git a/NEWS b/NEWS
index 83d082afad..40964d2ee0 100644
--- a/NEWS
+++ b/NEWS
@@ -21,6 +21,9 @@ Major new features:
 
 * PRIb* and PRIB* macros from C2X have been added to <inttypes.h>.
 
+* A new tunable, glibc.pthread.stack_hugetlb, can be used to disable
+  Transparent Huge Pages (THP) in stack allocation at pthread_create.
+
 Deprecated and removed features, and other changes affecting compatibility:
 
 * In the Linux kernel for the hppa/parisc architecture some of the
diff --git a/manual/tunables.texi b/manual/tunables.texi
index 70dd2264c5..130f94b2bc 100644
--- a/manual/tunables.texi
+++ b/manual/tunables.texi
@@ -459,6 +459,21 @@ registration on behalf of the application.
 Restartable sequences are a Linux-specific extension.
 @end deftp
 
+@deftp Tunable glibc.pthread.stack_hugetlb
+This tunable controls whether to use Huge Pages in the stacks created by
+@code{pthread_create}.  This tunable only affects the stacks created by
+@theglibc{}, it has no effect on stack assigned with
+@code{pthread_attr_setstack}.
+
+The default is @samp{1} where the system default value is used.  Setting
+its value to @code{0} enables the use of @code{madvise} with
+@code{MADV_NOHUGEPAGE} after stack creation with @code{mmap}.
+
+This is a memory utilization optimization, since internal glibc setup of either
+the thread descriptor and the guard page might force the kernel to move the
+thread stack originally backup by Huge Pages to default pages.
+@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 9133384d47..6517899718 100644
--- a/nptl/pthread_mutex_conf.c
+++ b/nptl/pthread_mutex_conf.c
@@ -44,6 +44,12 @@ 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)
 {
@@ -51,4 +57,6 @@ __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));
 }
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
+    }
   }
 }
-- 
2.38.1

Re: [PATCH v6 1/1] Created tunable to force small pages on stack allocation.

[Florian Weimer]

* Cupertino Miranda via Libc-alpha:

> 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.

Is this for the benefit of OpenJDK (among other things)?

In this case, we should expose this in a pthread_attr_t interface as
well, so that OpenJDK can activate this easily for the required threads.
This can be done in a follow-up patch.

Thanks,
Florian

Re: [PATCH v6 1/1] Created tunable to force small pages on stack allocation.

[Cupertino Miranda]

>> 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.
>
> Is this for the benefit of OpenJDK (among other things)?
Yes, it is actually. ;-)
>
> In this case, we should expose this in a pthread_attr_t interface as
> well, so that OpenJDK can activate this easily for the required threads.
> This can be done in a follow-up patch.
Totally aggree.
Our initial concern in proposing such change was to avoid big API
discussions when we were not sure if there was other simpler solution to
the problem.

I will work on such patches shortly if you think it is a good idea.

Thanks,
Cupertino

Re: [PATCH v6 1/1] Created tunable to force small pages on stack allocation.

[Adhemerval Zanella Netto]

On 14/04/23 12:12, 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.
> 
> Changes from v3:
>  - Improve tunables.texi.
> 
> Changes from v4:
>  - Improved text in tunables.texi by suggestion of Adhemerval.
> 
> Changes from v5:
>  - Added a new entry in NEWS.

LGTM, thanks.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

> ---
>  NEWS                          |  3 +++
>  manual/tunables.texi          | 15 +++++++++++++++
>  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 ++++++
>  7 files changed, 42 insertions(+)
> 
> diff --git a/NEWS b/NEWS
> index 83d082afad..40964d2ee0 100644
> --- a/NEWS
> +++ b/NEWS
> @@ -21,6 +21,9 @@ Major new features:
>  
>  * PRIb* and PRIB* macros from C2X have been added to <inttypes.h>.
>  
> +* A new tunable, glibc.pthread.stack_hugetlb, can be used to disable
> +  Transparent Huge Pages (THP) in stack allocation at pthread_create.
> +
>  Deprecated and removed features, and other changes affecting compatibility:
>  
>  * In the Linux kernel for the hppa/parisc architecture some of the
> diff --git a/manual/tunables.texi b/manual/tunables.texi
> index 70dd2264c5..130f94b2bc 100644
> --- a/manual/tunables.texi
> +++ b/manual/tunables.texi
> @@ -459,6 +459,21 @@ registration on behalf of the application.
>  Restartable sequences are a Linux-specific extension.
>  @end deftp
>  
> +@deftp Tunable glibc.pthread.stack_hugetlb
> +This tunable controls whether to use Huge Pages in the stacks created by
> +@code{pthread_create}.  This tunable only affects the stacks created by
> +@theglibc{}, it has no effect on stack assigned with
> +@code{pthread_attr_setstack}.
> +
> +The default is @samp{1} where the system default value is used.  Setting
> +its value to @code{0} enables the use of @code{madvise} with
> +@code{MADV_NOHUGEPAGE} after stack creation with @code{mmap}.
> +
> +This is a memory utilization optimization, since internal glibc setup of either
> +the thread descriptor and the guard page might force the kernel to move the
> +thread stack originally backup by Huge Pages to default pages.
> +@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 9133384d47..6517899718 100644
> --- a/nptl/pthread_mutex_conf.c
> +++ b/nptl/pthread_mutex_conf.c
> @@ -44,6 +44,12 @@ 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)
>  {
> @@ -51,4 +57,6 @@ __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));
>  }
> 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
> +    }
>    }
>  }

Re: [PATCH v6 1/1] Created tunable to force small pages on stack allocation.

[Cupertino Miranda]

Thanks !

Adhemerval Zanella Netto writes:

> On 14/04/23 12:12, 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.
>>
>> Changes from v3:
>>  - Improve tunables.texi.
>>
>> Changes from v4:
>>  - Improved text in tunables.texi by suggestion of Adhemerval.
>>
>> Changes from v5:
>>  - Added a new entry in NEWS.
>
> LGTM, thanks.
>
> Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
>
>> ---
>>  NEWS                          |  3 +++
>>  manual/tunables.texi          | 15 +++++++++++++++
>>  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 ++++++
>>  7 files changed, 42 insertions(+)
>>
>> diff --git a/NEWS b/NEWS
>> index 83d082afad..40964d2ee0 100644
>> --- a/NEWS
>> +++ b/NEWS
>> @@ -21,6 +21,9 @@ Major new features:
>>
>>  * PRIb* and PRIB* macros from C2X have been added to <inttypes.h>.
>>
>> +* A new tunable, glibc.pthread.stack_hugetlb, can be used to disable
>> +  Transparent Huge Pages (THP) in stack allocation at pthread_create.
>> +
>>  Deprecated and removed features, and other changes affecting compatibility:
>>
>>  * In the Linux kernel for the hppa/parisc architecture some of the
>> diff --git a/manual/tunables.texi b/manual/tunables.texi
>> index 70dd2264c5..130f94b2bc 100644
>> --- a/manual/tunables.texi
>> +++ b/manual/tunables.texi
>> @@ -459,6 +459,21 @@ registration on behalf of the application.
>>  Restartable sequences are a Linux-specific extension.
>>  @end deftp
>>
>> +@deftp Tunable glibc.pthread.stack_hugetlb
>> +This tunable controls whether to use Huge Pages in the stacks created by
>> +@code{pthread_create}.  This tunable only affects the stacks created by
>> +@theglibc{}, it has no effect on stack assigned with
>> +@code{pthread_attr_setstack}.
>> +
>> +The default is @samp{1} where the system default value is used.  Setting
>> +its value to @code{0} enables the use of @code{madvise} with
>> +@code{MADV_NOHUGEPAGE} after stack creation with @code{mmap}.
>> +
>> +This is a memory utilization optimization, since internal glibc setup of either
>> +the thread descriptor and the guard page might force the kernel to move the
>> +thread stack originally backup by Huge Pages to default pages.
>> +@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 9133384d47..6517899718 100644
>> --- a/nptl/pthread_mutex_conf.c
>> +++ b/nptl/pthread_mutex_conf.c
>> @@ -44,6 +44,12 @@ 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)
>>  {
>> @@ -51,4 +57,6 @@ __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));
>>  }
>> 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
>> +    }
>>    }
>>  }

Re: [PATCH v6 1/1] Created tunable to force small pages on stack allocation.

[Adhemerval Zanella Netto]

On 20/04/23 17:21, Cupertino Miranda wrote:
> 
> Thanks !
> 
> Adhemerval Zanella Netto writes:

I also sent an updated patch to detect when the split will always
happen [1].  As I wrote in the patch, the tunable might still be
required in some specific scenarios, but it would be good to have
some heuristic to detect such scenarios if/when distros start to
active THP to be always enabled.

[1] https://patchwork.sourceware.org/project/glibc/patch/20230420172436.2013698-1-adhemerval.zanella@linaro.org/

Re: [PATCH v6 1/1] Created tunable to force small pages on stack allocation.

[Cupertino Miranda]

> I also sent an updated patch to detect when the split will always
> happen [1].  As I wrote in the patch, the tunable might still be
> required in some specific scenarios, but it would be good to have
> some heuristic to detect such scenarios if/when distros start to
> active THP to be always enabled.
>
> [1] https://patchwork.sourceware.org/project/glibc/patch/20230420172436.2013698-1-adhemerval.zanella@linaro.org/
>
I have seen it and agree that it is useful.
I will attempt to test it tomorrow if you would be interested in the
feedback. I presume the condition is very similar to what I tested
before.

[PATCH v6 0/1] *** Created tunable to force small pages on stack allocation.

[Cupertino Miranda]

Hi,

This is supposedly the final version.
Added NEWS entry as requested by Adhemerval.

Regards,
Cupertino

Cupertino Miranda (1):
  Created tunable to force small pages on stack allocation.

 NEWS                          |  3 +++
 manual/tunables.texi          | 15 +++++++++++++++
 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 ++++++
 7 files changed, 42 insertions(+)

-- 
2.38.1