The patch titled Subject: fs: check bh blocknr earlier when searching lru has been added to the -mm tree. Its filename is fs-check-bh-blocknr-earlier-when-searching-lru.patch This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/fs-check-bh-blocknr-earlier-when-searching-lru.patch and later at http://ozlabs.org/~akpm/mmotm/broken-out/fs-check-bh-blocknr-earlier-when-searching-lru.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Zach Brown <zab@xxxxxxxxx> Subject: fs: check bh blocknr earlier when searching lru It's very common for the buffer heads in the lru to have different block numbers. By comparing the blocknr before the bdev and size we can reduce the cost of searching in the very common case where all the entries have the same bdev and size. In quick hot cache cycle counting tests on a single fs workstation this cut the cost of a miss by about 20%. A diff of the disassembly shows the reordering of the bdev and blocknr comparisons. This is in such a tiny loop that skipping one comparison is a meaningful portion of the total work being done: 1628: 83 c1 01 add $0x1,%ecx 162b: 83 f9 08 cmp $0x8,%ecx 162e: 74 60 je 1690 <__find_get_block+0xa0> 1630: 89 c8 mov %ecx,%eax 1632: 65 4c 8b 04 c5 00 00 mov %gs:0x0(,%rax,8),%r8 1639: 00 00 163b: 4d 85 c0 test %r8,%r8 163e: 4c 89 c3 mov %r8,%rbx 1641: 74 e5 je 1628 <__find_get_block+0x38> - 1643: 4d 3b 68 30 cmp 0x30(%r8),%r13 + 1643: 4d 3b 68 18 cmp 0x18(%r8),%r13 1647: 75 df jne 1628 <__find_get_block+0x38> - 1649: 4d 3b 60 18 cmp 0x18(%r8),%r12 + 1649: 4d 3b 60 30 cmp 0x30(%r8),%r12 164d: 75 d9 jne 1628 <__find_get_block+0x38> 164f: 49 39 50 20 cmp %rdx,0x20(%r8) 1653: 75 d3 jne 1628 <__find_get_block+0x38> Signed-off-by: Zach Brown <zab@xxxxxxxxx> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- fs/buffer.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff -puN fs/buffer.c~fs-check-bh-blocknr-earlier-when-searching-lru fs/buffer.c --- a/fs/buffer.c~fs-check-bh-blocknr-earlier-when-searching-lru +++ a/fs/buffer.c @@ -1331,8 +1331,8 @@ lookup_bh_lru(struct block_device *bdev, for (i = 0; i < BH_LRU_SIZE; i++) { struct buffer_head *bh = __this_cpu_read(bh_lrus.bhs[i]); - if (bh && bh->b_bdev == bdev && - bh->b_blocknr == block && bh->b_size == size) { + if (bh && bh->b_blocknr == block && bh->b_bdev == bdev && + bh->b_size == size) { if (i) { while (i) { __this_cpu_write(bh_lrus.bhs[i], _ Patches currently in -mm which might be from zab@xxxxxxxxx are fs-check-bh-blocknr-earlier-when-searching-lru.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html