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Commit 09eb47a7 authored by Frederic Weisbecker's avatar Frederic Weisbecker
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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 <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: default avatarFrederic Weisbecker <fweisbec@gmail.com>
parent b1c839bb

fs/reiserfs/stree.c

+11 −1
Original line number Original line Diff line number Diff line
@@ -529,6 +529,14 @@ static void search_by_key_reada(struct super_block *s, 
	for (i = 0; i < num; i++) {

	for (i = 0; i < num; i++) {

		bh[i] = sb_getblk(s, b[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++) {

	for (j = 0; j < i; j++) {

		/*

		/*

		 * note, this needs attention if we are getting rid of the BKL

		 * 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 =

		if ((bh = last_element->pe_buffer =

		     sb_getblk(sb, block_number))) {

		     sb_getblk(sb, block_number))) {

			if (!buffer_uptodate(bh) && reada_count > 1)

			if (!buffer_uptodate(bh) && reada_count > 1)

				/* will unlock the write lock */

				search_by_key_reada(sb, reada_bh,

				search_by_key_reada(sb, reada_bh,

						    reada_blocks, reada_count);

						    reada_blocks, reada_count);

			ll_rw_block(READ, 1, &bh);

			else

				reiserfs_write_unlock(sb);

				reiserfs_write_unlock(sb);

			ll_rw_block(READ, 1, &bh);

			wait_on_buffer(bh);

			wait_on_buffer(bh);

			reiserfs_write_lock(sb);

			reiserfs_write_lock(sb);

			if (!buffer_uptodate(bh))

			if (!buffer_uptodate(bh))