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Expand comments for malloc(9) to better describe the design and

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statistics / memory types model.
This commit is contained in:
Robert Watson 2006-07-23 19:51:39 +00:00
parent fb6d736d14
commit 0ce3f16dbb
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=160598
1 changed files with 44 additions and 8 deletions
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52
sys/kern/kern_malloc.c
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@ -31,6 +31,17 @@
* @(#)kern_malloc.c 8.3 (Berkeley) 1/4/94
*/
/*
* Kernel malloc(9) implementation -- general purpose kernel memory allocator
* based on memory types. Back end is implemented using the UMA(9) zone
* allocator. A set of fixed-size buckets are used for smaller allocations,
* and a special UMA allocation interface is used for larger allocations.
* Callers declare memory types, and statistics are maintained independently
* for each memory type. Statistics are maintained per-CPU for performance
* reasons. See malloc(9) and comments in malloc.h for a detailed
* description.
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
@ -85,6 +96,9 @@ __FBSDID("$FreeBSD$");
#define REALLOC_FRACTION 1 /* new block if <= half the size */
#endif
/*
* Centrally define some common malloc types.
*/
MALLOC_DEFINE(M_CACHE, "cache", "Various Dynamically allocated caches");
MALLOC_DEFINE(M_DEVBUF, "devbuf", "device driver memory");
MALLOC_DEFINE(M_TEMP, "temp", "misc temporary data buffers");
@ -110,7 +124,14 @@ static int kmemcount;
#define KMEM_ZSIZE (KMEM_ZMAX >> KMEM_ZSHIFT)
static u_int8_t kmemsize[KMEM_ZSIZE + 1];
/* These won't be powers of two for long */
/*
* Small malloc(9) memory allocations are allocated from a set of UMA buckets
* of various sizes.
*
* XXX: The comment here used to read "These won't be powers of two for
* long." It's possible that a significant amount of wasted memory could be
* recovered by tuning the sizes of these buckets.
*/
struct {
int kz_size;
char *kz_name;
@ -143,6 +164,14 @@ struct {
{0, NULL},
};
/*
* Zone to allocate malloc type descriptions from. For ABI reasons, memory
* types are described by a data structure passed by the declaring code, but
* the malloc(9) implementation has its own data structure describing the
* type and statistics. This permits the malloc(9)-internal data structures
* to be modified without breaking binary-compiled kernel modules that
* declare malloc types.
*/
static uma_zone_t mt_zone;
u_int vm_kmem_size;
@ -160,7 +189,6 @@ SYSCTL_UINT(_vm, OID_AUTO, kmem_size_scale, CTLFLAG_RD, &vm_kmem_size_scale, 0,
/*
* The malloc_mtx protects the kmemstatistics linked list.
*/
struct mtx malloc_mtx;
#ifdef MALLOC_PROFILE
@ -172,14 +200,16 @@ static int sysctl_kern_mprof(SYSCTL_HANDLER_ARGS);
static int sysctl_kern_malloc(SYSCTL_HANDLER_ARGS);
static int sysctl_kern_malloc_stats(SYSCTL_HANDLER_ARGS);
/* time_uptime of last malloc(9) failure */
/*
* time_uptime of the last malloc(9) failure (induced or real).
*/
static time_t t_malloc_fail;
#ifdef MALLOC_MAKE_FAILURES
/*
* Causes malloc failures every (n) mallocs with M_NOWAIT. If set to 0,
* doesn't cause failures.
* malloc(9) fault injection -- cause malloc failures every (n) mallocs when
* the caller specifies M_NOWAIT. If set to 0, no failures are caused.
*/
#ifdef MALLOC_MAKE_FAILURES
SYSCTL_NODE(_debug, OID_AUTO, malloc, CTLFLAG_RD, 0,
"Kernel malloc debugging options");
@ -201,7 +231,10 @@ malloc_last_fail(void)
}
/*
* Add this to the informational malloc_type bucket.
* An allocation has succeeded -- update malloc type statistics for the
* amount of bucket size. Occurs within a critical section so that the
* thread isn't preempted and doesn't migrate while updating per-PCU
* statistics.
*/
static void
malloc_type_zone_allocated(struct malloc_type *mtp, unsigned long size,
@ -231,7 +264,10 @@ malloc_type_allocated(struct malloc_type *mtp, unsigned long size)
}
/*
* Remove this allocation from the informational malloc_type bucket.
* A free operation has occurred -- update malloc type statistis for the
* amount of the bucket size. Occurs within a critical section so that the
* thread isn't preempted and doesn't migrate while updating per-CPU
* statistics.
*/
void
malloc_type_freed(struct malloc_type *mtp, unsigned long size)