Re: [PATCH v2] nptl: Invert the mmap/mprotect logic on allocated stacks (BZ#18988)

[Adhemerval Zanella <adhemerval dot zanella at linaro dot org>]

Ping.

On 06/02/2017 18:49, Adhemerval Zanella wrote:
> This is an update from my previous patch [1].  Then change from previous
> version are:
> 
>   - Create inline functions for guard page address calculation and
>     segments protection setup;
>   - Fix an issue for downwards stack allocation.
> 
> --
> 
> Current allocate_stack logic for create stacks is to first mmap all
> the required memory with the desirable memory and then mprotect the
> guard area with PROT_NONE if required.  Although it works as expected,
> it pessimizes the allocation because it requires the kernel to actually
> increase commit charge (it counts against the available physical/swap
> memory available for the system).
> 
> The only issue is to actually check this change since side-effects are
> really Linux specific and to actually account them it would require a
> kernel specific tests to parse the system wide information.  On the kernel
> I checked /proc/self/statm does not show any meaningful difference for
> vmm and/or rss before and after thread creation.  I could only see
> really meaningful information checking on system wide /proc/meminfo
> between thread creation: MemFree, MemAvailable, and Committed_AS shows
> large difference without the patch.  I think trying to use these
> kind of information on a testcase is fragile.
> 
> The BZ#18988 reports shows that the commit pages are easily seen with
> mlockall (MCL_FUTURE) (with lock all pages that become mapped in the
> process) however a more straighfoward testcase shows that pthread_create
> could be faster using this patch:
> 
> --
> static const int inner_count = 256;
> static const int outer_count = 128;
> 
> static
> void *thread1(void *arg)
> {
>   return NULL;
> }
> 
> static
> void *sleeper(void *arg)
> {
>   pthread_t ts[inner_count];
>   for (int i = 0; i < inner_count; i++)
>     pthread_create (&ts[i], &a, thread1, NULL);
>   for (int i = 0; i < inner_count; i++)
>     pthread_join (ts[i], NULL);
> 
>   return NULL;
> }
> 
> int main(void)
> {
>   pthread_attr_init(&a);
>   pthread_attr_setguardsize(&a, 1<<20);
>   pthread_attr_setstacksize(&a, 1134592);
> 
>   pthread_t ts[outer_count];
>   for (int i = 0; i < outer_count; i++)
>     pthread_create(&ts[i], &a, sleeper, NULL);
>   for (int i = 0; i < outer_count; i++)
>     pthread_join(ts[i], NULL);
>     assert(r == 0);
>   }
>   return 0;
> }
> 
> --
> 
> On x86_64 (4.4.0-45-generic, gcc 5.4.0) running the small benchtests
> I see:
> 
> $ time ./test
> 
> real	0m3.647s
> user	0m0.080s
> sys	0m11.836s
> 
> While with the patch I see:
> 
> $ time ./test
> 
> real	0m0.696s
> user	0m0.040s
> sys	0m1.152s
> 
> So I added a pthread_create benchtest (thread_create) which check
> the thread creation latency.  As for the simple benchtests, I saw
> improvements in thread creation on all architectures I tested the
> change.
> 
> Checked on x86_64-linux-gnu, i686-linux-gnu, aarch64-linux-gnu,
> arm-linux-gnueabihf, and powerpc64le-linux-gnu.
> 
> 	[BZ #18988]
> 	* benchtests/thread_create-inputs: New file.
> 	* benchtests/thread_create-source.c: Likewise.
> 	* support/xpthread_attr_setguardsize.c: Likewise.
> 	* support/Makefile (libsupport-routines): Add
> 	xpthread_attr_setguardsize object.
> 	* support/xthread.h: Add xpthread_attr_setguardsize prototype.
> 	* benchtests/Makefile (bench-pthread): Add thread_create.
> 	* nptl/allocatestack.c (allocate_stack): Call mmap with PROT_NONE and
> 	then mprotect the required area.
> 
> [1] https://sourceware.org/ml/libc-alpha/2017-02/msg00033.html
> 
> ---
>  ChangeLog                            | 13 +++++++
>  benchtests/Makefile                  |  2 +-
>  benchtests/thread_create-inputs      | 14 ++++++++
>  benchtests/thread_create-source.c    | 58 +++++++++++++++++++++++++++++++
>  nptl/allocatestack.c                 | 66 +++++++++++++++++++++++++++++++-----
>  support/Makefile                     |  1 +
>  support/xpthread_attr_setguardsize.c | 26 ++++++++++++++
>  support/xthread.h                    |  2 ++
>  8 files changed, 173 insertions(+), 9 deletions(-)
>  create mode 100644 benchtests/thread_create-inputs
>  create mode 100644 benchtests/thread_create-source.c
>  create mode 100644 support/xpthread_attr_setguardsize.c
> 
> diff --git a/ChangeLog b/ChangeLog
> index 710f9b4..8a81549 100644
> --- a/ChangeLog
> +++ b/ChangeLog
> @@ -1,5 +1,18 @@
>  2016-02-06  Adhemerval Zanella  <adhemerval.zanella@linaro.org>
>  
> +	[BZ #18988]
> +	* benchtests/thread_create-inputs: New file.
> +	* benchtests/thread_create-source.c: Likewise.
> +	* support/xpthread_attr_setguardsize.c: Likewise.
> +	* support/Makefile (libsupport-routines): Add
> +	xpthread_attr_setguardsize object.
> +	* support/xthread.h: Add xpthread_attr_setguardsize prototype.
> +	* benchtests/Makefile (bench-pthread): Add thread_create.
> +	* nptl/allocatestack.c (allocate_stack): Call mmap with PROT_NONE and
> +	then mprotect the required area.
> +	(guard_position): New function.
> +	(setup_stack_prot): Likewise.
> +
>  	* nptl/allocatestack.c [COLORING_INCREMENT] (nptl_ncreated): Remove.
>  	(allocate_stack): Remove COLORING_INCREMENT usage.
>  	* nptl/stack-aliasing.h (COLORING_INCREMENT). Likewise.
> diff --git a/benchtests/Makefile b/benchtests/Makefile
> index 81edf8a..6535373 100644
> --- a/benchtests/Makefile
> +++ b/benchtests/Makefile
> @@ -25,7 +25,7 @@ bench-math := acos acosh asin asinh atan atanh cos cosh exp exp2 log log2 \
>  	      modf pow rint sin sincos sinh sqrt tan tanh fmin fmax fminf \
>  	      fmaxf
>  
> -bench-pthread := pthread_once
> +bench-pthread := pthread_once thread_create
>  
>  bench-string := ffs ffsll
>  
> diff --git a/benchtests/thread_create-inputs b/benchtests/thread_create-inputs
> new file mode 100644
> index 0000000..e3ca03b
> --- /dev/null
> +++ b/benchtests/thread_create-inputs
> @@ -0,0 +1,14 @@
> +## args: int:size_t:size_t
> +## init: thread_create_init
> +## includes: pthread.h
> +## include-sources: thread_create-source.c
> +
> +## name: stack=1024,guard=1
> +32, 1024, 1
> +## name: stack=1024,guard=2
> +32, 1024, 2
> +
> +## name: stack=2048,guard=1
> +32, 2048, 1
> +## name: stack=2048,guard=2
> +32, 2048, 2
> diff --git a/benchtests/thread_create-source.c b/benchtests/thread_create-source.c
> new file mode 100644
> index 0000000..74e7777
> --- /dev/null
> +++ b/benchtests/thread_create-source.c
> @@ -0,0 +1,58 @@
> +/* Measure pthread_create thread creation with different stack
> +   and guard sizes.
> +
> +   Copyright (C) 2017 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <http://www.gnu.org/licenses/>.  */
> +
> +#include <stdio.h>
> +#include <unistd.h>
> +#include <support/xthread.h>
> +
> +static size_t pgsize;
> +
> +static void
> +thread_create_init (void)
> +{
> +  pgsize = sysconf (_SC_PAGESIZE);
> +}
> +
> +static void *
> +thread_dummy (void *arg)
> +{
> +  return NULL;
> +}
> +
> +static void
> +thread_create (int nthreads, size_t stacksize, size_t guardsize)
> +{
> +  pthread_attr_t attr;
> +  xpthread_attr_init (&attr);
> +
> +  stacksize = stacksize * pgsize;
> +  guardsize = guardsize * pgsize;
> +  
> +  xpthread_attr_setstacksize (&attr, stacksize);
> +  xpthread_attr_setguardsize (&attr, guardsize);
> +
> +  pthread_t ts[nthreads];
> +
> +  for (int i = 0; i < nthreads; i++)
> +    ts[i] = xpthread_create (&attr, thread_dummy, NULL);
> +
> +  for (int i = 0; i < nthreads; i++)
> +    xpthread_join (ts[i]);
> +}
> diff --git a/nptl/allocatestack.c b/nptl/allocatestack.c
> index e5c5f79..8364406 100644
> --- a/nptl/allocatestack.c
> +++ b/nptl/allocatestack.c
> @@ -334,6 +334,43 @@ change_stack_perm (struct pthread *pd
>    return 0;
>  }
>  
> +/* Return the guard page position on allocated stack.  */
> +static inline char *
> +__attribute ((always_inline))
> +guard_position (void *mem, size_t size, size_t guardsize, struct pthread *pd,
> +		size_t pagesize_m1)
> +{
> +#ifdef NEED_SEPARATE_REGISTER_STACK
> +  return mem + (((size - guardsize) / 2) & ~pagesize_m1);
> +#elif _STACK_GROWS_DOWN
> +  return mem;
> +#elif _STACK_GROWS_UP
> +  return (char *) (((uintptr_t) pd - guardsize) & ~pagesize_m1);
> +#endif
> +}
> +
> +/* Based on stack allocated with PROT_NONE, setup the required portions with
> +   'prot' flags based on the guard page position.  */
> +static inline int
> +setup_stack_prot (char *mem, size_t size, char *guard, size_t guardsize,
> +		  const int prot)
> +{
> +  char *guardend = guard + guardsize;
> +#if _STACK_GROWS_DOWN
> +  /* As defined at guard_position, for architectures with downward stack
> +     the guard page is always at start of the allocated area.  */
> +  if (mprotect (guardend, size - guardsize, prot) != 0)
> +    return errno;
> +#else
> +  size_t mprots1 = (uintptr_t) guard - (uintptr_t) mem;
> +  if (mprotect (mem, mprots1, prot) != 0)
> +    return errno;
> +  size_t mprots2 = ((uintptr_t) mem + size) - (uintptr_t) guardend;
> +  if (mprotect (guardend, mprots2, prot) != 0)
> +    return errno;
> +#endif
> +  return 0;
> +}
>  
>  /* Returns a usable stack for a new thread either by allocating a
>     new stack or reusing a cached stack of sufficient size.
> @@ -490,7 +527,10 @@ allocate_stack (const struct pthread_attr *attr, struct pthread **pdp,
>  	    size += pagesize_m1 + 1;
>  #endif
>  
> -	  mem = mmap (NULL, size, prot,
> +	  /* If a guard page is required, avoid committing memory by first
> +	     allocate with PROT_NONE and then reserve with required permission
> +	     excluding the guard page.  */
> +	  mem = mmap (NULL, size, (guardsize == 0) ? prot : PROT_NONE,
>  		      MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0);
>  
>  	  if (__glibc_unlikely (mem == MAP_FAILED))
> @@ -510,9 +550,24 @@ allocate_stack (const struct pthread_attr *attr, struct pthread **pdp,
>  				   - TLS_PRE_TCB_SIZE);
>  #endif
>  
> +	  /* Now mprotect the required region excluding the guard area.  */
> +	  if (__glibc_likely (guardsize > 0))
> +	    {
> +	      char *guard = guard_position (mem, size, guardsize, pd,
> +					    pagesize_m1);
> +	      if (setup_stack_prot (mem, size, guard, guardsize, prot) != 0)
> +		{
> +		  munmap (mem, size);
> +		  return errno;
> +		}
> +	    }
> +
>  	  /* Remember the stack-related values.  */
>  	  pd->stackblock = mem;
>  	  pd->stackblock_size = size;
> +	  /* Update guardsize for newly allocated guardsize to avoid
> +	     an mprotect in guard resize below.  */
> +	  pd->guardsize = guardsize;
>  
>  	  /* We allocated the first block thread-specific data array.
>  	     This address will not change for the lifetime of this
> @@ -593,13 +648,8 @@ allocate_stack (const struct pthread_attr *attr, struct pthread **pdp,
>        /* Create or resize the guard area if necessary.  */
>        if (__glibc_unlikely (guardsize > pd->guardsize))
>  	{
> -#ifdef NEED_SEPARATE_REGISTER_STACK
> -	  char *guard = mem + (((size - guardsize) / 2) & ~pagesize_m1);
> -#elif _STACK_GROWS_DOWN
> -	  char *guard = mem;
> -#elif _STACK_GROWS_UP
> -	  char *guard = (char *) (((uintptr_t) pd - guardsize) & ~pagesize_m1);
> -#endif
> +	  char *guard = guard_position (mem, size, guardsize, pd,
> +					pagesize_m1);
>  	  if (mprotect (guard, guardsize, PROT_NONE) != 0)
>  	    {
>  	    mprot_error:
> diff --git a/support/Makefile b/support/Makefile
> index 2ace559..c0a443f 100644
> --- a/support/Makefile
> +++ b/support/Makefile
> @@ -68,6 +68,7 @@ libsupport-routines = \
>    xpthread_attr_init \
>    xpthread_attr_setdetachstate \
>    xpthread_attr_setstacksize \
> +  xpthread_attr_setguardsize \
>    xpthread_barrier_destroy \
>    xpthread_barrier_init \
>    xpthread_barrier_wait \
> diff --git a/support/xpthread_attr_setguardsize.c b/support/xpthread_attr_setguardsize.c
> new file mode 100644
> index 0000000..35fed5d
> --- /dev/null
> +++ b/support/xpthread_attr_setguardsize.c
> @@ -0,0 +1,26 @@
> +/* pthread_attr_setguardsize with error checking.
> +   Copyright (C) 2017 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <http://www.gnu.org/licenses/>.  */
> +
> +#include <support/xthread.h>
> +
> +void
> +xpthread_attr_setguardsize (pthread_attr_t *attr, size_t guardsize)
> +{
> +  xpthread_check_return ("pthread_attr_setguardize",
> +			 pthread_attr_setguardsize (attr, guardsize));
> +}
> diff --git a/support/xthread.h b/support/xthread.h
> index 6dd7e70..3552a73 100644
> --- a/support/xthread.h
> +++ b/support/xthread.h
> @@ -67,6 +67,8 @@ void xpthread_attr_setdetachstate (pthread_attr_t *attr,
>  				   int detachstate);
>  void xpthread_attr_setstacksize (pthread_attr_t *attr,
>  				 size_t stacksize);
> +void xpthread_attr_setguardsize (pthread_attr_t *attr,
> +				 size_t guardsize);
>  
>  /* This function returns non-zero if pthread_barrier_wait returned
>     PTHREAD_BARRIER_SERIAL_THREAD.  */
>