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