* [PATCH v6 1/1] Created tunable to force small pages on stack allocation.
2023-04-14 14:28 [PATCH v6 0/1] *** Created tunable to force small pages on stack allocation Cupertino Miranda
@ 2023-04-14 14:28 ` Cupertino Miranda
0 siblings, 0 replies; 3+ messages in thread
From: Cupertino Miranda @ 2023-04-14 14:28 UTC (permalink / raw)
To: libc-alpha; +Cc: jose.marchesi, elena.zannoni, 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 c54af824e0..941808049a 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 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
+ }
}
}
--
2.38.1
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