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kill-the-bkl/reiserfs: reduce number of contentions in search_by_key()

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search_by_key() is a central function in reiserfs which searches
the patch in the fs tree from the root to a node given its key.

It is the function that is most requesting the write lock
because it's a path very often used.

Also we forget to release the lock while reading the next tree node,
making us holding the lock in a wasteful way.

Then we release the lock while reading the current node and its childs,
all-in-one. It should be safe because we have a reference to these
blocks and even if we read a block that will be concurrently changed,
we have an fs_changed check later that will make us retry the path from
the root.

[ Impact: release the write lock while unused in a hot path ]

Cc: Jeff Mahoney <jeffm@suse.com>
Cc: Chris Mason <chris.mason@oracle.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Alexander Beregalov <a.beregalov@gmail.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
This commit is contained in:
Frederic Weisbecker 2009-05-08 14:21:33 +02:00
parent b1c839bb2d
commit 09eb47a7c5
1 changed files with 11 additions and 1 deletions
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12
fs/reiserfs/stree.c
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@ -529,6 +529,14 @@ static void search_by_key_reada(struct super_block *s,
for (i = 0; i < num; i++) {
bh[i] = sb_getblk(s, b[i]);
}
/*
* We are going to read some blocks on which we
* have a reference. It's safe, though we might be
* reading blocks concurrently changed if we release
* the lock. But it's still fine because we check later
* if the tree changed
*/
reiserfs_write_unlock(s);
for (j = 0; j < i; j++) {
/*
* note, this needs attention if we are getting rid of the BKL
@ -626,10 +634,12 @@ int search_by_key(struct super_block *sb, const struct cpu_key *key, /* Key to s
if ((bh = last_element->pe_buffer =
sb_getblk(sb, block_number))) {
if (!buffer_uptodate(bh) && reada_count > 1)
/* will unlock the write lock */
search_by_key_reada(sb, reada_bh,
reada_blocks, reada_count);
else
reiserfs_write_unlock(sb);
ll_rw_block(READ, 1, &bh);
reiserfs_write_unlock(sb);
wait_on_buffer(bh);
reiserfs_write_lock(sb);
if (!buffer_uptodate(bh))