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Subject[PATCH] dm-writecache: avoid unnecessary lookups in writecache_find_entry
Date
From: Huaisheng Ye <yehs1@lenovo.com>

Only when entry has been found, that would only be necessary to check the
lowest or highest seq-count.

Add local variable "found" in writecache_find_entry, if no entry has been
found, it is meaningless that having a useless rb_prev or rb_next.

Signed-off-by: Huaisheng Ye <yehs1@lenovo.com>
---
drivers/md/dm-writecache.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/md/dm-writecache.c b/drivers/md/dm-writecache.c
index ddf1732..047ae09 100644
--- a/drivers/md/dm-writecache.c
+++ b/drivers/md/dm-writecache.c
@@ -537,14 +537,18 @@ static struct wc_entry *writecache_find_entry(struct dm_writecache *wc,
{
struct wc_entry *e;
struct rb_node *node = wc->tree.rb_node;
+ bool found = false;

if (unlikely(!node))
return NULL;

while (1) {
e = container_of(node, struct wc_entry, rb_node);
- if (read_original_sector(wc, e) == block)
+ if (read_original_sector(wc, e) == block) {
+ found = true;
break;
+ }
+
node = (read_original_sector(wc, e) >= block ?
e->rb_node.rb_left : e->rb_node.rb_right);
if (unlikely(!node)) {
@@ -564,7 +568,8 @@ static struct wc_entry *writecache_find_entry(struct dm_writecache *wc,
}
}

- while (1) {
+ /* only need to check lowest or highest seq-count when entry has been found */
+ while (found) {
struct wc_entry *e2;
if (flags & WFE_LOWEST_SEQ)
node = rb_prev(&e->rb_node);
@@ -577,6 +582,9 @@ static struct wc_entry *writecache_find_entry(struct dm_writecache *wc,
return e;
e = e2;
}
+
+ /* no entry has been found, return the following entry */
+ return e;
}

static void writecache_insert_entry(struct dm_writecache *wc, struct wc_entry *ins)
--
1.8.3.1

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