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SubjectRe: [PATCH] slab.c cleanup
Anton wrote:

>> - Don't create caches that are not multiples of L1_CACHE_BYTES.
>
>Nice idea, I often see the list walk (of the cache sizes) in kmalloc in kernel
>profiles. eg a bunch of kmalloc(2k) for network drivers.
>
>Since we have a 128byte cacheline on ppc64 this patch should reduce that.
>
>
No, the patch is a bad thing: It means that everyone who does
kmalloc(32,) now allocates 128 bytes, i.e. 3/4 wasted. IMHO not acceptable.

I agree that the list walk in kmalloc is a problem - but the right
solution is a quicker lookup.
Perhaps something like the attached patch.
For networking: I bet that virtually all allocations have the same size
- what about calling kmem_find_general_cachep, and caching the last
request/result? Then the next calls can allocate directly from the
appropriate cache, without any lookup.

--
Manfred

--- 2.5/mm/slab.c Sat Oct 26 21:13:33 2002
+++ build-2.5/mm/slab.c Sun Oct 27 13:48:06 2002
@@ -424,6 +430,7 @@
CN("size-131072")
};
#undef CN
+static struct cache_sizes *malloc_hints[sizeof(size_t)*8];

struct arraycache_init initarray_cache __initdata = { { 0, BOOT_CPUCACHE_ENTRIES, 1, 0} };
struct arraycache_init initarray_generic __initdata = { { 0, BOOT_CPUCACHE_ENTRIES, 1, 0} };
@@ -587,6 +594,7 @@
void __init kmem_cache_init(void)
{
size_t left_over;
+ int i;

init_MUTEX(&cache_chain_sem);
INIT_LIST_HEAD(&cache_chain);
@@ -604,6 +612,18 @@
* that initializes ac_data for all new cpus
*/
register_cpu_notifier(&cpucache_notifier);
+
+ for (i=0;i<sizeof(size_t)*8;i++) {
+ struct cache_sizes *csizep = malloc_sizes;
+ int size = (1<<i)+1;
+
+ for ( ; csizep->cs_size; csizep++) {
+ if (size > csizep->cs_size)
+ continue;
+ break;
+ }
+ malloc_hints[i] = csizep;
+ }
}


@@ -1796,7 +1816,11 @@
*/
void * kmalloc (size_t size, int flags)
{
- struct cache_sizes *csizep = malloc_sizes;
+ struct cache_sizes *csizep;
+
+ if (unlikely(size < 2))
+ size = 2;
+ csizep = malloc_hints[fls((size-1))-1];

for (; csizep->cs_size; csizep++) {
if (size > csizep->cs_size)
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