Btrfs devel - Sep 2007 - [patch]Cache blocks in the hole at beginning of a block group

Hi

When first extent item in a block group isn't at beginning of that
block group,  blocks in the hole (at beginning of a block group) is
free.

Regards
YZ

diff -r 9cb5f0f5c713 extent-tree.c
--- a/extent-tree.c	Thu Aug 30 12:16:51 2007 -0400
+++ b/extent-tree.c	Tue Sep 11 22:59:56 2007 +0800
@@ -102,15 +102,14 @@ static int cache_block_group(struct btrf
 		}
 		if (btrfs_key_type(&key) == BTRFS_EXTENT_ITEM_KEY) {
 			if (!found) {
-				last = key.objectid + key.offset;
+				last = block_group->key.objectid;
 				found = 1;
-			} else {
-				hole_size = key.objectid - last;
-				for (i = 0; i < hole_size; i++) {
-					set_radix_bit(extent_radix, last + i);
-				}
-				last = key.objectid + key.offset;
-			}
+			}
+			hole_size = key.objectid - last;
+			for (i = 0; i < hole_size; i++) {
+				set_radix_bit(extent_radix, last + i);
+			}
+			last = key.objectid + key.offset;
 		}
 		path->slots[0]++;
 	}
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On Tue, 11 Sep 2007 23:26:40 +0800
"Yan Zheng" <yanzheng@21cn.com> wrote:
> Hi
> 
> When first extent item in a block group isn't at beginning of that
> block group,  blocks in the hole (at beginning of a block group) is
> free.
Thanks, you've definitely found a bug in the current code, but I'm
afraid we can't assume the start of the block group is free.  There
could be an extent allocated in the last block group that extends into
the current one.

So, we need to find the previous extent and make sure it doesn't
overlap.

-chris

Hello everyone.

Please consider this patch, the original one has duplicate codes in
the loop body. The only change in this one is move the duplicate codes
out from the loop body.

Regards
YZ

diff -r 0d4a5b197024 extent-tree.c
--- a/extent-tree.c	Tue Sep 11 19:45:31 2007 -0400
+++ b/extent-tree.c	Fri Sep 14 23:21:08 2007 +0800
@@ -39,6 +39,7 @@ static int cache_block_group(struct btrf
 	u64 i;
 	u64 last = 0;
 	u64 hole_size;
+	u64 first_free;
 	int found = 0;

 	root = root->fs_info->extent_root;
@@ -52,6 +53,7 @@ static int cache_block_group(struct btrf
 	if (!path)
 		return -ENOMEM;
 	path->reada = 2;
+	first_free = block_group->key.objectid;
 	key.objectid = block_group->key.objectid;
 	key.flags = 0;
 	key.offset = 0;
@@ -71,50 +73,45 @@ static int cache_block_group(struct btrf
 			if (ret == 0) {
 				continue;
 			} else {
-				if (found) {
-					hole_size = block_group->key.objectid +
-						block_group->key.offset - last;
-				} else {
-					last = block_group->key.objectid;
-					hole_size = block_group->key.offset;
-				}
-				for (i = 0; i < hole_size; i++) {
-					set_radix_bit(extent_radix,
-						      last + i);
-				}
 				break;
 			}
 		}
 		btrfs_disk_key_to_cpu(&key, &leaf->items[slot].key);
+		if (key.objectid < block_group->key.objectid) {
+			if (key.objectid + key.offset > first_free)
+				first_free = key.objectid + key.offset;
+			goto next;
+		}
 		if (key.objectid >= block_group->key.objectid +
 		    block_group->key.offset) {
-			if (found) {
-				hole_size = block_group->key.objectid +
-					block_group->key.offset - last;
-			} else {
-				last = block_group->key.objectid;
-				hole_size = block_group->key.offset;
-			}
+			break;
+		}
+		if (btrfs_key_type(&key) == BTRFS_EXTENT_ITEM_KEY) {
+			if (!found) {
+				last = first_free;
+				found = 1;
+			}
+			hole_size = key.objectid - last;
 			for (i = 0; i < hole_size; i++) {
 				set_radix_bit(extent_radix, last + i);
 			}
-			break;
-		}
-		if (btrfs_key_type(&key) == BTRFS_EXTENT_ITEM_KEY) {
-			if (!found) {
-				last = key.objectid + key.offset;
-				found = 1;
-			} else {
-				hole_size = key.objectid - last;
-				for (i = 0; i < hole_size; i++) {
-					set_radix_bit(extent_radix, last + i);
-				}
-				last = key.objectid + key.offset;
-			}
-		}
+			last = key.objectid + key.offset;
+		}
+next:
 		path->slots[0]++;
 	}

+	if (!found)
+		last = first_free;
+	if (block_group->key.objectid +
+	    block_group->key.offset > last) {
+		hole_size = block_group->key.objectid +
+			block_group->key.offset - last;
+		for (i = 0; i < hole_size; i++) {
+			set_radix_bit(extent_radix,
+					last + i);
+		}
+	}
 	block_group->cached = 1;
 err:
 	btrfs_free_path(path);
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