From 09eb47a7c52ad535aafca889e0b936c445c375ce Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Fri, 8 May 2009 14:21:33 +0200 Subject: [PATCH] kill-the-bkl/reiserfs: reduce number of contentions in search_by_key() 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 Cc: Chris Mason Cc: Ingo Molnar Cc: Alexander Beregalov Signed-off-by: Frederic Weisbecker --- fs/reiserfs/stree.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/fs/reiserfs/stree.c b/fs/reiserfs/stree.c index 6ddcecb4e8a..960c9114f6d 100644 --- a/fs/reiserfs/stree.c +++ b/fs/reiserfs/stree.c @@ -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))