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vm: add alignment parameter to cache allocator

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caches with object size N, where N is a power of two, will naturally
align their objects on N-byte boundaries.

all other caches will align to an 8-byte boundary by default.
This commit is contained in:
max 🍓
2023-02-06 20:41:40 +00:00
parent 109616ec30
commit 5c7bde4fdf
3 changed files with 27 additions and 7 deletions
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2
include/socks/util.h
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@@ -2,7 +2,9 @@
#define SOCKS_UTIL_H_
#include <stddef.h>
#include <stdbool.h>
extern void data_size_to_string(size_t value, char *out, size_t outsz);
static inline bool power_of_2(size_t x) { return (x > 0 && (x & (x - 1)) == 0); }
#endif

6
include/socks/vm.h
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@@ -137,9 +137,11 @@ typedef struct vm_cache {
unsigned int c_obj_size;
/* combined size of vm_slab_t and the freelist */
unsigned int c_hdr_size;
/* power of 2 alignment for objects returned from the cache */
unsigned int c_align;
/* offset from one object to the next in a slab.
this may be different from c_obj_size as
we enforce a 16-byte alignment on allocated objects */
this may be different from c_obj_size depending
on the alignment settings for this cache. */
unsigned int c_stride;
/* size of page used for slabs */
unsigned int c_page_order;

26
vm/cache.c
View File

@@ -1,7 +1,8 @@
#include <socks/queue.h>
#include <socks/compiler.h>
#include <stddef.h>
#include <socks/vm.h>
#include <socks/util.h>
#include <stddef.h>
#define FREELIST_END ((unsigned int)-1)
@@ -31,13 +32,19 @@ void vm_cache_init(vm_cache_t *cache)
cache->c_flags |= VM_CACHE_OFFSLAB;
}
if (power_of_2(cache->c_obj_size)) {
cache->c_align = cache->c_obj_size;
} else {
cache->c_align = 8;
}
size_t available = vm_page_order_to_bytes(cache->c_page_order);
size_t space_per_item = cache->c_obj_size;
/* align to 16-byte boundary */
if (space_per_item & 0xF) {
space_per_item &= ~0xF;
space_per_item += 0x10;
/* align to specified boundary */
if (space_per_item & (cache->c_align - 1)) {
space_per_item &= ~(cache->c_align - 1);
space_per_item += cache->c_align;
}
cache->c_stride = space_per_item;
@@ -55,6 +62,15 @@ void vm_cache_init(vm_cache_t *cache)
cache->c_slabs_empty = QUEUE_INIT;
cache->c_hdr_size = sizeof(vm_slab_t) + (sizeof(unsigned int) * cache->c_obj_count);
/* for on-slab caches, c_hdr_size is added to the slab pointer to
get the object buffer pointer. by aligning c_hdr_size to the
requested alignment, we ensure that the object buffer
is aligned too */
if (cache->c_hdr_size & (cache->c_align - 1)) {
cache->c_hdr_size &= ~(cache->c_align - 1);
cache->c_hdr_size += cache->c_align;
}
}
void vm_cache_destroy(vm_cache_t *cache)