The patch titled
SLUB: use ilog2 instead of series of constant comparisons
has been added to the -mm tree. Its filename is
slub-use-ilog2-instead-of-series-of-constant-comparisons.patch
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: SLUB: use ilog2 instead of series of constant comparisons
From: Christoph Lameter <clameter@xxxxxxx>
I finally found a way to get rid of the nasty list of comparisions in
slub_def.h. ilog2 seems to work right for constants.
Also update comments
Drop the generation of an unresolved symbol for the case that the size is
too big. A simple BUG_ON sufficies now that we can alloc up to MAX_ORDER
size slab objects.
Signed-off-by: Christoph Lameter <clameter@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/slub_def.h | 66 +++++++++++--------------------------
1 files changed, 20 insertions(+), 46 deletions(-)
diff -puN include/linux/slub_def.h~slub-use-ilog2-instead-of-series-of-constant-comparisons include/linux/slub_def.h
--- a/include/linux/slub_def.h~slub-use-ilog2-instead-of-series-of-constant-comparisons
+++ a/include/linux/slub_def.h
@@ -10,6 +10,7 @@
#include <linux/gfp.h>
#include <linux/workqueue.h>
#include <linux/kobject.h>
+#include <linux/log2.h>
struct kmem_cache_node {
spinlock_t list_lock; /* Protect partial list and nr_partial */
@@ -58,6 +59,8 @@ struct kmem_cache {
*/
#define KMALLOC_SHIFT_LOW 3
+#define KMALLOC_MIN_SIZE (1UL << KMALLOC_SHIFT_LOW)
+
/*
* We keep the general caches in an array of slab caches that are used for
* 2^x bytes of allocations.
@@ -65,56 +68,36 @@ struct kmem_cache {
extern struct kmem_cache kmalloc_caches[KMALLOC_SHIFT_HIGH + 1];
/*
- * Sorry that the following has to be that ugly but some versions of GCC
- * have trouble with constant propagation and loops.
+ * Determine the kmalloc array index given the object size.
+ *
+ * Return -1 if the object size is not supported.
*/
static inline int kmalloc_index(size_t size)
{
/*
- * We should return 0 if size == 0 but we use the smallest object
- * here for SLAB legacy reasons.
+ * We should return 0 if size == 0 (which would result in the
+ * kmalloc caller to get NULL) but we use the smallest object
+ * here for legacy reasons. Just issue a warning so that
+ * we can discover locations where we do 0 sized allocations.
*/
WARN_ON_ONCE(size == 0);
if (size > KMALLOC_MAX_SIZE)
return -1;
+ if (size <= KMALLOC_MIN_SIZE)
+ return KMALLOC_SHIFT_LOW;
+
+ /*
+ * We map the non power of two slabs to the unused
+ * log2 values in the kmalloc array.
+ */
if (size > 64 && size <= 96)
return 1;
if (size > 128 && size <= 192)
return 2;
- if (size <= 8) return 3;
- if (size <= 16) return 4;
- if (size <= 32) return 5;
- if (size <= 64) return 6;
- if (size <= 128) return 7;
- if (size <= 256) return 8;
- if (size <= 512) return 9;
- if (size <= 1024) return 10;
- if (size <= 2 * 1024) return 11;
- if (size <= 4 * 1024) return 12;
- if (size <= 8 * 1024) return 13;
- if (size <= 16 * 1024) return 14;
- if (size <= 32 * 1024) return 15;
- if (size <= 64 * 1024) return 16;
- if (size <= 128 * 1024) return 17;
- if (size <= 256 * 1024) return 18;
- if (size <= 512 * 1024) return 19;
- if (size <= 1024 * 1024) return 20;
- if (size <= 2 * 1024 * 1024) return 21;
- if (size <= 4 * 1024 * 1024) return 22;
- if (size <= 8 * 1024 * 1024) return 23;
- if (size <= 16 * 1024 * 1024) return 24;
- if (size <= 32 * 1024 * 1024) return 25;
- return -1;
-/*
- * What we really wanted to do and cannot do because of compiler issues is:
- * int i;
- * for (i = KMALLOC_SHIFT_LOW; i <= KMALLOC_SHIFT_HIGH; i++)
- * if (size <= (1 << i))
- * return i;
- */
+ return ilog2(size - 1) + 1;
}
/*
@@ -131,18 +114,9 @@ static inline struct kmem_cache *kmalloc
return NULL;
/*
- * This function only gets expanded if __builtin_constant_p(size), so
- * testing it here shouldn't be needed. But some versions of gcc need
- * help.
+ * If this triggers then the amount of memory requested was too large.
*/
- if (__builtin_constant_p(size) && index < 0) {
- /*
- * Generate a link failure. Would be great if we could
- * do something to stop the compile here.
- */
- extern void __kmalloc_size_too_large(void);
- __kmalloc_size_too_large();
- }
+ BUG_ON(index < 0);
return &kmalloc_caches[index];
}
_
Patches currently in -mm which might be from clameter@xxxxxxx are
slub-debug-fix-object-size-calculation.patch
git-ubi.patch
quicklist-support-for-x86_64.patch
slub-debug-fix-check-for-super-sized-slabs-512k-64bit-256k.patch
change-zonelist-order-zonelist-order-selection-logic.patch
change-zonelist-order-zonelist-order-selection-logic-add-check_highest_zone-to-build_zonelists_in_zone_order.patch
change-zonelist-order-v6-zonelist-fix.patch
change-zonelist-order-auto-configuration.patch
change-zonelist-order-documentaion.patch
make-proc-slabinfo-use-seq_list_xxx-helpers.patch
remove-the-deprecated-kmem_cache_t-typedef-from-slabh.patch
slub-use-ilog2-instead-of-series-of-constant-comparisons.patch
add-__gfp_movable-for-callers-to-flag-allocations-from-high-memory-that-may-be-migrated-mark-bio_alloc-allocations-correctly.patch
add-__gfp_movable-for-callers-to-flag-allocations-from-high-memory-that-may-be-migrated-rename-gfp_high_movable-to-gfp_highuser_movable.patch
add-__gfp_movable-for-callers-to-flag-allocations-from-high-memory-that-may-be-migrated-mark-page-cache-pages-as-__gfp_pagecache-instead-of-__gfp_movable.patch
group-short-lived-and-reclaimable-kernel-allocations-use-slab_account_reclaim-to-determine-when-__gfp_reclaimable-should-be-used.patch
group-short-lived-and-reclaimable-kernel-allocations-use-slab_account_reclaim-to-determine-when-__gfp_reclaimable-should-be-used-fix.patch
group-short-lived-and-reclaimable-kernel-allocations-do-not-annotate-shmem-allocations-explicitly.patch
group-short-lived-and-reclaimable-kernel-allocations-add-__gfp_temporary-to-identify-allocations-that-are-short-lived.patch
have-kswapd-keep-a-minimum-order-free-other-than-order-0.patch
have-kswapd-keep-a-minimum-order-free-other-than-order-0-fix.patch
only-check-absolute-watermarks-for-alloc_high-and-alloc_harder-allocations.patch
slub-mm-only-make-slub-the-default-slab-allocator.patch
slub-exploit-page-mobility-to-increase-allocation-order.patch
slub-reduce-antifrag-max-order.patch
slub-reduce-antifrag-max-order-use-antifrag-constant-instead-of-hardcoding-page-order.patch
revoke-core-code.patch
mm-implement-swap-prefetching.patch
rename-gfp_high_movable-to-gfp_highuser_movable-prefetch.patch
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