ocfs2: throttle back local alloc when low on disk space

Ocfs2's local allocator disables itself for the duration of a mount point
when it has trouble allocating a large enough area from the primary bitmap.
That can cause performance problems, especially for disks which were only
temporarily full or fragmented. This patch allows for the allocator to
shrink it's window first, before being disabled. Later, it can also be
re-enabled so that any performance drop is minimized.

To do this, we allow the value of osb->local_alloc_bits to be shrunk when
needed. The default value is recorded in a mostly read-only variable so that
we can re-initialize when required.

Locking had to be updated so that we could protect changes to
local_alloc_bits. Mostly this involves protecting various local alloc values
with the osb spinlock. A new state is also added, OCFS2_LA_THROTTLED, which
is used when the local allocator is has shrunk, but is not disabled. If the
available space dips below 1 megabyte, the local alloc file is disabled. In
either case, local alloc is re-enabled 30 seconds after the event, or when
an appropriate amount of bits is seen in the primary bitmap.

Signed-off-by: Mark Fasheh <mfasheh@suse.com>

1 files changed, 19 insertions, 4 deletions

diff --git a/fs/ocfs2/ocfs2.h b/fs/ocfs2/ocfs2.h
index 43dd42e313a1..4d6e200a4843 100644
--- a/fs/ocfs2/ocfs2.h
+++ b/fs/ocfs2/ocfs2.h
@@ -171,9 +171,13 @@ struct ocfs2_alloc_stats
 
 enum ocfs2_local_alloc_state
 {
-	OCFS2_LA_UNUSED = 0,
-	OCFS2_LA_ENABLED,
-	OCFS2_LA_DISABLED
+	OCFS2_LA_UNUSED = 0,	/* Local alloc will never be used for
+				 * this mountpoint. */
+	OCFS2_LA_ENABLED,	/* Local alloc is in use. */
+	OCFS2_LA_THROTTLED,	/* Local alloc is in use, but number
+				 * of bits has been reduced. */
+	OCFS2_LA_DISABLED	/* Local alloc has temporarily been
+				 * disabled. */
 };
 
 enum ocfs2_mount_options
@@ -252,9 +256,20 @@ struct ocfs2_super
 	struct ocfs2_journal *journal;
 	unsigned long osb_commit_interval;
 
+	struct delayed_work		la_enable_wq;
+
+	/*
+	 * Must hold local alloc i_mutex and osb->osb_lock to change
+	 * local_alloc_bits. Reads can be done under either lock.
+	 */
 	unsigned int local_alloc_bits;
-	enum ocfs2_local_alloc_state local_alloc_state;
+	unsigned int local_alloc_default_bits;
+
+	enum ocfs2_local_alloc_state local_alloc_state; /* protected
+							 * by osb_lock */
+
 	struct buffer_head *local_alloc_bh;
+
 	u64 la_last_gd;
 
 	/* Next two fields are for local node slot recovery during