tree a5bd28e558b889ad7c026199f6032b2ff33f9103
parent c63e3c0b2498adec921b06c670d12c8c74b85538
author Frederic Weisbecker <fweisbec@gmail.com> 1242262599 +0200
committer Frederic Weisbecker <fweisbec@gmail.com> 1252905502 +0200

kill-the-bkl/reiserfs: unlock only when needed in search_by_key

search_by_key() is the site which most requires the lock.
This is mostly because it is a very central function and also
because it releases/reaqcuires the write lock at least once each
time it is called.

Such release/reacquire creates a lot of contention in this place and
also opens more the window which let another thread changing the tree.
When it happens, the current path searching over the tree must be
retried from the beggining (the root) which is a wasteful and
time consuming recovery.

This patch factorizes two release/reacquire sequences:

- reading leaf nodes blocks
- reading current block

The latter immediately follows the former.

The whole sequence is safe as a single unlocked section because
we check just after if the tree has changed during these operations.

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>