From: Minfei Huang <mnfhuang@xxxxxxxxx>
There is a buffer_head lru list cache in local cpu to accelerate the
speed. The LRU management algorithm is simple enough in
bh_lru_install().
There are three situtaions we should deal with.
1) All/part of the lru cache is NULL.
2) The new buffer_head hitts the lru cache.
3) The new buffer_head does hit the lru cache.
We put the new buffer_head at the head of lru cache, then copy the
buffer_head from the original lru cache, and drop the spare.
Signed-off-by: Minfei Huang <mnfhuang@xxxxxxxxx>
---
fs/buffer.c | 32 ++++++++++++++++++++------------
1 file changed, 20 insertions(+), 12 deletions(-)
diff --git a/fs/buffer.c b/fs/buffer.c
index 1cf7a53..2139574 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1287,8 +1287,6 @@ static inline void check_irqs_on(void)
*/
static void bh_lru_install(struct buffer_head *bh)
{
- struct buffer_head *evictee = NULL;
-
check_irqs_on();
bh_lru_lock();
if (__this_cpu_read(bh_lrus.bhs[0]) != bh) {
@@ -1302,25 +1300,35 @@ static void bh_lru_install(struct buffer_head *bh)
struct buffer_head *bh2 =
__this_cpu_read(bh_lrus.bhs[in]);
- if (bh2 == bh) {
+ if (bh2 == NULL) {
+ /* Rest value in bh_lrus.bhs always is NULL */
+ break;
+ } else if (bh2 == bh) {
__brelse(bh2);
} else {
- if (out >= BH_LRU_SIZE) {
- BUG_ON(evictee != NULL);
- evictee = bh2;
+ if (out == BH_LRU_SIZE) {
+ /*
+ * this condition will be happened,
+ * only if none of entry in
+ * bh_lrus.bhs hits the new bh,
+ * so the last bh should be released.
+ */
+ BUG_ON(in != BH_LRU_SIZE - 1);
+ __brelse(bh2);
+ break;
} else {
bhs[out++] = bh2;
}
}
}
- while (out < BH_LRU_SIZE)
- bhs[out++] = NULL;
- memcpy(this_cpu_ptr(&bh_lrus.bhs), bhs, sizeof(bhs));
+ /*
+ * it is fine that the value out may be smaller than
+ * BH_LRU_SIZE. The rest of the value in bh_lrus.bhs is NULL.
+ */
+ memcpy(this_cpu_ptr(&bh_lrus.bhs), bhs,
+ sizeof(struct buffer_head *) * out);
}
bh_lru_unlock();
-
- if (evictee)
- __brelse(evictee);
}
/*
--
2.1.0
--
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