On 29.06.21 г. 16:59, Josef Bacik wrote:
> I've been debugging an early ENOSPC problem in production and finally
> root caused it to this problem. When we switched to the per-inode in
> 38d715f494f2 ("btrfs: use btrfs_start_delalloc_roots in
> shrink_delalloc") I pulled out the async extent handling, because we
> were doing the correct thing by calling filemap_flush() if we had async
> extents set. This would properly wait on any async extents by locking
> the page in the second flush, thus making sure our ordered extents were
> properly set up.
>
> However when I switched us back to page based flushing, I used
> sync_inode(), which allows us to pass in our own wbc. The problem here
> is that sync_inode() is smarter than the filemap_* helpers, it tries to
> avoid calling writepages at all. This means that our second call could
> skip calling do_writepages altogether, and thus not wait on the pagelock
> for the async helpers. This means we could come back before any ordered
> extents were created and then simply continue on in our flushing
> mechanisms and ENOSPC out when we have plenty of space to use.
>
> Fix this by putting back the async pages logic in shrink_delalloc. This
> allows us to bulk write out everything that we need to, and then we can
> wait in one place for the async helpers to catch up, and then wait on
> any ordered extents that are created.
>
> Fixes: e076ab2a2ca7 ("btrfs: shrink delalloc pages instead of full inodes")
> Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
This patch really depend on the next one in order for it to be correct.
Imo this dependency should be explicitly stated in the change log and
the patches re-ordered.
