Peter Zijlstra wrote:
On Fri, 2008-11-14 at 11:17 +0200, Pekka J Enberg wrote:
From: Pekka Enberg <penberg@xxxxxxxxxxxxxx>
As spotted by kmemtrace, struct ext2_sb_info is 17024 bytes and ext3_sb_info is
17152 bytes on 64-bit which makes them a very bad fit for SLAB allocators. In
fact, both allocations are round up to the next available page size of
order 3 which is 32 KB.
The culprit if the wasted memory is the ->s_blockgroup_lock which can be as big
as 16 KB when CONFIG_NR_CPUS is set to 32. As struct blockgroup_lock is a
perfect fit for order 2 page in the worst case, allocate ->s_blockgroup_lock
separately to avoid wasting space.
And here I was thinking that NR_CPUS=4096 is currently our worst
case ;-)
Sure but look at <linux/blockgroup_lock.h>. NR_BG_LOCKS is capped to 128
for >= 32 CPUs.
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