Patch "Btrfs: fix early ENOSPC due to delalloc" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

Btrfs: fix early ENOSPC due to delalloc

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
btrfs-fix-early-enospc-due-to-delalloc.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Omar Sandoval <[email protected]>
Date: Thu, 20 Jul 2017 15:10:35 -0700
Subject: Btrfs: fix early ENOSPC due to delalloc

From: Omar Sandoval <[email protected]>

commit 17024ad0a0fdfcfe53043afb969b813d3e020c21 upstream.

If a lot of metadata is reserved for outstanding delayed allocations, we rely on shrink_delalloc() to reclaim metadata space in order to fulfill reservation tickets. However, shrink_delalloc() has a shortcut where if it determines that space can be overcommitted, it will stop early. This made sense before the ticketed enospc system, but now it means that shrink_delalloc() will often not reclaim enough space to fulfill any tickets, leading to an early ENOSPC. (Reservation tickets don't care about being able to overcommit, they need every byte accounted for.)

Fix it by getting rid of the shortcut so that shrink_delalloc() reclaims all of the metadata it is supposed to. This fixes early ENOSPCs we were seeing when doing a btrfs receive to populate a new filesystem, as well as early ENOSPCs Christoph saw when doing a big cp -r onto Btrfs.

---
 fs/btrfs/extent-tree.c |    4 ----
 1 file changed, 4 deletions(-)

@@ -4759,10 +4759,6 @@ skip_async:
 		else
 			flush = BTRFS_RESERVE_NO_FLUSH;
 		spin_lock(&space_info->lock);
-		if (can_overcommit(root, space_info, orig, flush)) {
-			spin_unlock(&space_info->lock);
-			break;
-		}
 		if (list_empty(&space_info->tickets) &&
 		    list_empty(&space_info->priority_tickets)) {
 			spin_unlock(&space_info->lock);

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/btrfs-fix-early-enospc-due-to-delalloc.patch