From: Josef Bacik <jbacik@fb.com>
Date: Thu, 1 Oct 2015 16:55:18 +0000 (-0400)
Subject: Btrfs: don't continue setting up space cache when enospc
X-Git-Tag: v4.4-rc1~18^2~31^2~4
X-Git-Url: http://git.cascardo.eti.br/?a=commitdiff_plain;h=2968b1f48bd7366dd7310acde1ee6d1bf7791142;p=cascardo%2Flinux.git

Btrfs: don't continue setting up space cache when enospc

If we hit ENOSPC when setting up a space cache don't bother setting up any of
the other space cache's in this transaction, it'll just induce unnecessary
latency.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>
---

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index febb5bc35a64..3185c457f025 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3402,6 +3402,15 @@ again:
 	}
 	spin_unlock(&block_group->lock);
 
+	/*
+	 * We hit an ENOSPC when setting up the cache in this transaction, just
+	 * skip doing the setup, we've already cleared the cache so we're safe.
+	 */
+	if (test_bit(BTRFS_TRANS_CACHE_ENOSPC, &trans->transaction->flags)) {
+		ret = -ENOSPC;
+		goto out_put;
+	}
+
 	/*
 	 * Try to preallocate enough space based on how big the block group is.
 	 * Keep in mind this has to include any pinned space which could end up
@@ -3422,8 +3431,18 @@ again:
 	ret = btrfs_prealloc_file_range_trans(inode, trans, 0, 0, num_pages,
 					      num_pages, num_pages,
 					      &alloc_hint);
+	/*
+	 * Our cache requires contiguous chunks so that we don't modify a bunch
+	 * of metadata or split extents when writing the cache out, which means
+	 * we can enospc if we are heavily fragmented in addition to just normal
+	 * out of space conditions.  So if we hit this just skip setting up any
+	 * other block groups for this transaction, maybe we'll unpin enough
+	 * space the next time around.
+	 */
 	if (!ret)
 		dcs = BTRFS_DC_SETUP;
+	else if (ret == -ENOSPC)
+		set_bit(BTRFS_TRANS_CACHE_ENOSPC, &trans->transaction->flags);
 	btrfs_free_reserved_data_space(inode, num_pages);
 
 out_put:
diff --git a/fs/btrfs/transaction.h b/fs/btrfs/transaction.h
index 109b8b7fb48e..30ae75074ca4 100644
--- a/fs/btrfs/transaction.h
+++ b/fs/btrfs/transaction.h
@@ -34,6 +34,7 @@ enum btrfs_trans_state {
 
 #define BTRFS_TRANS_HAVE_FREE_BGS	0
 #define BTRFS_TRANS_DIRTY_BG_RUN	1
+#define BTRFS_TRANS_CACHE_ENOSPC	2
 
 struct btrfs_transaction {
 	u64 transid;