OK, I know this is really just a micro optimization, but I figured I'd
submit it anyway. Looking into the slab code, I came across the
cache_estimate function, which has the following code:
i = 0;
while (i*size + ALIGN(base+i*extra, align) <= wastage)
i++;
if (i > 0)
i--;
Now this is counting linearly up and will be O(n) for n = number of
objects in the page order. Since objects range up to 202 (according to
my /proc/slabinfo). So I figured there must be a better way. So I added
this:
i = 0;
do {
x = 1;
while ((x+i)*size + ALIGN(base+(x+i)*extra, align) <= wastage)
x <<= 1;
i += (x >> 1);
} while (x > 1);
Which now makes it O(log n). This basically does a binary search for
the upper range. I tested this code in userspace, and it works just the
same as the original code, but with less iterations.
I know this is really a micro optimization, but if you think every usec
counts, then we can use this patch ;)
-- Steve
Index: linux-2.6.15-rc5/mm/slab.c
===================================================================
--- linux-2.6.15-rc5.orig/mm/slab.c 2005-12-16 16:24:09.000000000 -0500
+++ linux-2.6.15-rc5/mm/slab.c 2005-12-18 03:16:18.000000000 -0500
@@ -700,6 +700,7 @@
int flags, size_t *left_over, unsigned int *num)
{
int i;
+ int x;
size_t wastage = PAGE_SIZE<<gfporder;
size_t extra = 0;
size_t base = 0;
@@ -709,10 +710,12 @@
extra = sizeof(kmem_bufctl_t);
}
i = 0;
- while (i*size + ALIGN(base+i*extra, align) <= wastage)
- i++;
- if (i > 0)
- i--;
+ do {
+ x = 1;
+ while ((x+i)*size + ALIGN(base+(x+i)*extra, align) <= wastage)
+ x <<= 1;
+ i += (x >> 1);
+ } while (x > 1);
if (i > SLAB_LIMIT)
i = SLAB_LIMIT;
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
