From 4366211ccd050e00674b3276b5ed81981b2d7793 Mon Sep 17 00:00:00 2001
From: Chris Mason <chris.mason@oracle.com>
Date: Fri, 7 Nov 2008 09:06:11 -0500
Subject: [PATCH] Btfs: More metadata allocator optimizations

This lowers the empty cluster target for metadata allocations.  The lower
target makes it easier to do allocations and still seems to perform well.

It also fixes the allocator loop to drop the empty cluster when things
start getting difficult, avoiding false enospc warnings.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
---
 fs/btrfs/extent-tree.c | 28 ++++++++++++++++++----------
 1 file changed, 18 insertions(+), 10 deletions(-)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index b8c6541c33fe..0d73a53c6763 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -2116,6 +2116,7 @@ static int noinline find_free_extent(struct btrfs_trans_handle *trans,
 	struct btrfs_root * root = orig_root->fs_info->extent_root;
 	u64 total_needed = num_bytes;
 	u64 *last_ptr = NULL;
+	u64 last_wanted = 0;
 	struct btrfs_block_group_cache *block_group = NULL;
 	int chunk_alloc_done = 0;
 	int empty_cluster = 2 * 1024 * 1024;
@@ -2134,22 +2135,28 @@ static int noinline find_free_extent(struct btrfs_trans_handle *trans,
 
 	if (data & BTRFS_BLOCK_GROUP_METADATA) {
 		last_ptr = &root->fs_info->last_alloc;
-		empty_cluster = 256 * 1024;
+		empty_cluster = 64 * 1024;
 	}
 
 	if ((data & BTRFS_BLOCK_GROUP_DATA) && btrfs_test_opt(root, SSD))
 		last_ptr = &root->fs_info->last_data_alloc;
 
 	if (last_ptr) {
-		if (*last_ptr)
+		if (*last_ptr) {
 			hint_byte = *last_ptr;
-		else
+			last_wanted = *last_ptr;
+		} else
 			empty_size += empty_cluster;
+	} else {
+		empty_cluster = 0;
 	}
 	search_start = max(search_start, first_logical_byte(root, 0));
 	search_start = max(search_start, hint_byte);
 	total_needed += empty_size;
 
+	if (search_start != last_wanted)
+		last_wanted = 0;
+
 	block_group = btrfs_lookup_block_group(root->fs_info, search_start);
 	if (!block_group)
 		block_group = btrfs_lookup_first_block_group(root->fs_info,
@@ -2195,9 +2202,9 @@ static int noinline find_free_extent(struct btrfs_trans_handle *trans,
 			if (search_start + num_bytes > end)
 				goto new_group;
 
-			if (last_ptr && *last_ptr && search_start != *last_ptr) {
+			if (last_wanted && search_start != last_wanted) {
 				total_needed += empty_cluster;
-				*last_ptr = 0;
+				last_wanted = 0;
 				/*
 				 * if search_start is still in this block group
 				 * then we just re-search this block group
@@ -2223,6 +2230,7 @@ static int noinline find_free_extent(struct btrfs_trans_handle *trans,
 				if (search_start >= start &&
 				    search_start < end) {
 					mutex_unlock(&block_group->alloc_mutex);
+					last_wanted = 0;
 					continue;
 				}
 
@@ -2240,6 +2248,11 @@ static int noinline find_free_extent(struct btrfs_trans_handle *trans,
 			break;
 		}
 new_group:
+		last_wanted = 0;
+		if (loop > 0) {
+			total_needed -= empty_cluster;
+			empty_cluster = 0;
+		}
 		mutex_unlock(&block_group->alloc_mutex);
 		/*
 		 * Here's how this works.
@@ -2256,11 +2269,6 @@ new_group:
 		if (loop == 0) {
 			head = &space_info->block_groups;
 			cur = head->next;
-
-			if (last_ptr && *last_ptr) {
-				total_needed += empty_cluster;
-				*last_ptr = 0;
-			}
 			loop++;
 		} else if (loop == 1 && cur == head) {
 			if (allowed_chunk_alloc && !chunk_alloc_done) {