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* malloc/malloc.c: Dynamically size mmap treshold if the program

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frees mmaped blocks.
	Patch by Valerie Henson and Arjan van de Ven.
This commit is contained in:
Ulrich Drepper 2006-08-09 21:51:56 +00:00
parent be7ffd91f8
commit 1d05c2fb9c
2 changed files with 87 additions and 1 deletions
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6
ChangeLog
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@ -1,3 +1,9 @@
2006-08-09 Ulrich Drepper <drepper@redhat.com>
* malloc/malloc.c: Dynamically size mmap treshold if the program
frees mmaped blocks.
Patch by Valerie Henson and Arjan van de Ven.
2006-08-08 Jakub Jelinek <jakub@redhat.com>
* sysdeps/unix/sysv/linux/ia64/bits/fcntl.h (O_DIRECT): Protect with

82
malloc/malloc.c
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@ -1414,6 +1414,19 @@ int __posix_memalign(void **, size_t, size_t);
#define DEFAULT_TOP_PAD (0)
#endif
/*
MMAP_THRESHOLD_MAX and _MIN are the bounds on the dynamically
adjusted MMAP_THRESHOLD.
*/
#ifndef DEFAULT_MMAP_THRESHOLD_MIN
#define DEFAULT_MMAP_THRESHOLD_MIN (128 * 1024)
#endif
#ifndef DEFAULT_MMAP_THRESHOLD_MAX
#define DEFAULT_MMAP_THRESHOLD_MAX (8 * 1024 * 1024 * sizeof(long))
#endif
/*
M_MMAP_THRESHOLD is the request size threshold for using mmap()
to service a request. Requests of at least this size that cannot
@ -1453,12 +1466,63 @@ int __posix_memalign(void **, size_t, size_t);
"large" chunks, but the value of "large" varies across systems. The
default is an empirically derived value that works well in most
systems.
Update in 2006:
The above was written in 2001. Since then the world has changed a lot.
Memory got bigger. Applications got bigger. The virtual address space
layout in 32 bit linux changed.
In the new situation, brk() and mmap space is shared and there are no
artificial limits on brk size imposed by the kernel. What is more,
applications have started using transient allocations larger than the
128Kb as was imagined in 2001.
The price for mmap is also high now; each time glibc mmaps from the
kernel, the kernel is forced to zero out the memory it gives to the
application. Zeroing memory is expensive and eats a lot of cache and
memory bandwidth. This has nothing to do with the efficiency of the
virtual memory system, by doing mmap the kernel just has no choice but
to zero.
In 2001, the kernel had a maximum size for brk() which was about 800
megabytes on 32 bit x86, at that point brk() would hit the first
mmaped shared libaries and couldn't expand anymore. With current 2.6
kernels, the VA space layout is different and brk() and mmap
both can span the entire heap at will.
Rather than using a static threshold for the brk/mmap tradeoff,
we are now using a simple dynamic one. The goal is still to avoid
fragmentation. The old goals we kept are
1) try to get the long lived large allocations to use mmap()
2) really large allocations should always use mmap()
and we're adding now:
3) transient allocations should use brk() to avoid forcing the kernel
having to zero memory over and over again
The implementation works with a sliding threshold, which is by default
limited to go between 128Kb and 32Mb (64Mb for 64 bitmachines) and starts
out at 128Kb as per the 2001 default.
This allows us to satisfy requirement 1) under the assumption that long
lived allocations are made early in the process' lifespan, before it has
started doing dynamic allocations of the same size (which will
increase the threshold).
The upperbound on the threshold satisfies requirement 2)
The threshold goes up in value when the application frees memory that was
allocated with the mmap allocator. The idea is that once the application
starts freeing memory of a certain size, it's highly probable that this is
a size the application uses for transient allocations. This estimator
is there to satisfy the new third requirement.
*/
#define M_MMAP_THRESHOLD -3
#ifndef DEFAULT_MMAP_THRESHOLD
#define DEFAULT_MMAP_THRESHOLD (128 * 1024)
#define DEFAULT_MMAP_THRESHOLD DEFAULT_MMAP_THRESHOLD_MIN
#endif
/*
@ -2251,6 +2315,10 @@ struct malloc_par {
int n_mmaps;
int n_mmaps_max;
int max_n_mmaps;
/* the mmap_threshold is dynamic, until the user sets
it manually, at which point we need to disable any
dynamic behavior. */
int no_dyn_threshold;
/* Cache malloc_getpagesize */
unsigned int pagesize;
@ -3428,6 +3496,14 @@ public_fREe(Void_t* mem)
#if HAVE_MMAP
if (chunk_is_mmapped(p)) /* release mmapped memory. */
{
/* see if the dynamic brk/mmap threshold needs adjusting */
if (!mp_.no_dyn_threshold
&& p->size > mp_.mmap_threshold
&& p->size <= DEFAULT_MMAP_THRESHOLD_MAX)
{
mp_.mmap_threshold = chunksize (p);
mp_.trim_threshold = 2 * mp_.mmap_threshold;
}
munmap_chunk(p);
return;
}
@ -5418,10 +5494,12 @@ int mALLOPt(param_number, value) int param_number; int value;
case M_TRIM_THRESHOLD:
mp_.trim_threshold = value;
mp_.no_dyn_threshold = 1;
break;
case M_TOP_PAD:
mp_.top_pad = value;
mp_.no_dyn_threshold = 1;
break;
case M_MMAP_THRESHOLD:
@ -5432,6 +5510,7 @@ int mALLOPt(param_number, value) int param_number; int value;
else
#endif
mp_.mmap_threshold = value;
mp_.no_dyn_threshold = 1;
break;
case M_MMAP_MAX:
@ -5441,6 +5520,7 @@ int mALLOPt(param_number, value) int param_number; int value;
else
#endif
mp_.n_mmaps_max = value;
mp_.no_dyn_threshold = 1;
break;
case M_CHECK_ACTION: