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authorEric Biggers <ebiggers@google.com>2017-07-10 15:47:29 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2017-07-10 16:32:30 -0700
commit241f01fbeda2521f802eeef4de0261387e6e9c1d (patch)
tree1ea0ec512f4f55fe1ade4c030d6b255f85c0e41a /fs/buffer.c
parent3457f4147675108aa83f9f33c136f06bb9f8518f (diff)
downloadlinux-241f01fbeda2521f802eeef4de0261387e6e9c1d.tar.bz2
fs/buffer.c: make bh_lru_install() more efficient
To install a buffer_head into the cpu's LRU queue, bh_lru_install() would construct a new copy of the queue and then memcpy it over the real queue. But it's easily possible to do the update in-place, which is faster and simpler. Some work can also be skipped if the buffer_head was already in the queue. As a microbenchmark I timed how long it takes to run sb_getblk() 10,000,000 times alternating between BH_LRU_SIZE + 1 blocks. Effectively, this benchmarks looking up buffer_heads that are in the page cache but not in the LRU: Before this patch: 1.758s After this patch: 1.653s This patch also removes about 350 bytes of compiled code (on x86_64), partly due to removal of the memcpy() which was being inlined+unrolled. Link: http://lkml.kernel.org/r/20161229193445.1913-1-ebiggers3@gmail.com Signed-off-by: Eric Biggers <ebiggers@google.com> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Christoph Lameter <cl@linux.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs/buffer.c')
-rw-r--r--fs/buffer.c43
1 files changed, 15 insertions, 28 deletions
diff --git a/fs/buffer.c b/fs/buffer.c
index ea0e05ec2916..5715dac7821f 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1281,44 +1281,31 @@ static inline void check_irqs_on(void)
}
/*
- * The LRU management algorithm is dopey-but-simple. Sorry.
+ * Install a buffer_head into this cpu's LRU. If not already in the LRU, it is
+ * inserted at the front, and the buffer_head at the back if any is evicted.
+ * Or, if already in the LRU it is moved to the front.
*/
static void bh_lru_install(struct buffer_head *bh)
{
- struct buffer_head *evictee = NULL;
+ struct buffer_head *evictee = bh;
+ struct bh_lru *b;
+ int i;
check_irqs_on();
bh_lru_lock();
- if (__this_cpu_read(bh_lrus.bhs[0]) != bh) {
- struct buffer_head *bhs[BH_LRU_SIZE];
- int in;
- int out = 0;
-
- get_bh(bh);
- bhs[out++] = bh;
- for (in = 0; in < BH_LRU_SIZE; in++) {
- struct buffer_head *bh2 =
- __this_cpu_read(bh_lrus.bhs[in]);
- if (bh2 == bh) {
- __brelse(bh2);
- } else {
- if (out >= BH_LRU_SIZE) {
- BUG_ON(evictee != NULL);
- evictee = bh2;
- } else {
- bhs[out++] = bh2;
- }
- }
+ b = this_cpu_ptr(&bh_lrus);
+ for (i = 0; i < BH_LRU_SIZE; i++) {
+ swap(evictee, b->bhs[i]);
+ if (evictee == bh) {
+ bh_lru_unlock();
+ return;
}
- while (out < BH_LRU_SIZE)
- bhs[out++] = NULL;
- memcpy(this_cpu_ptr(&bh_lrus.bhs), bhs, sizeof(bhs));
}
- bh_lru_unlock();
- if (evictee)
- __brelse(evictee);
+ get_bh(bh);
+ bh_lru_unlock();
+ brelse(evictee);
}
/*