Hi,
On 10/07/2016 09:24 PM, Josef Bacik wrote:
On 09/22/2016 05:25 AM, Wang Xiaoguang wrote:
Since commit b02441999efcc6152b87cd58e7970bb7843f76cf, we don't wait all
ordered extents, but I run into some enospc errors when doing large file
create and delete test, it's because shrink_delalloc() does not write
enough delalloc bytes and wait them finished:
From: Miao Xie <mi...@cn.fujitsu.com>
Date: Mon, 4 Nov 2013 23:13:25 +0800
Subject: [PATCH] Btrfs: don't wait for the completion of all the
ordered extents
It is very likely that there are lots of ordered extents in the
filesytem,
if we wait for the completion of all of them when we want to
reclaim some
space for the metadata space reservation, we would be blocked for
a long
time. The performance would drop down suddenly for a long time.
But since Josef introduced "Btrfs: introduce ticketed enospc
infrastructure",
shrink_delalloc() starts to be run asynchronously, then If we want to
reclaim
metadata space, we can try harder, after all, false enospc error is not
acceptable.
Signed-off-by: Wang Xiaoguang <wangxg.f...@cn.fujitsu.com>
---
fs/btrfs/extent-tree.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 46c2a37..f7c420b 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -4721,7 +4721,7 @@ static void shrink_delalloc(struct btrfs_root
*root, u64 to_reclaim, u64 orig,
if (trans)
return;
if (wait_ordered)
- btrfs_wait_ordered_roots(root->fs_info, items,
+ btrfs_wait_ordered_roots(root->fs_info, -1,
0, (u64)-1);
return;
}
@@ -4775,6 +4775,14 @@ skip_async:
}
delalloc_bytes = percpu_counter_sum_positive(
&root->fs_info->delalloc_bytes);
+ if (loops == 2) {
+ /*
+ * Try to write all current delalloc bytes and wait all
+ * ordered extents to have a last try.
+ */
+ to_reclaim = delalloc_bytes;
+ items = -1;
+ }
}
}
The problem is if the outstanding ordered extents aren't enough to
actually return the space we need we end up flushing and waiting
longer when we should have just committed the transaction. Think for
example if we are slowly writing to a few files and rapidly removing
thousands of files. In this case all of our space is tied up in
pinned, so we'd be better off not waiting on ordered extents and
instead committing the transaction.
Yes, I see, writing ordered extents are involved in disk writes, which
are much slow.
I think instead what we should do is have a priority set, so instead
of doing commit_cycles in btrfs_async_reclaim_metadata_space, we
instead have priority, and set it to say 3. Then we pass this
priority down to all of the flushers, and use it as a multiplier in
delalloc for the number of items we'll wait on. Once we hit priority 0
we wait for all the things. This way we do the easy pass first and
hope it works, if not we try harder the next time through, etc until
we throw all caution to the wind and wait for anything we can find.
Thanks,
OK, thanks for your suggestions, I'll try to write a better version, thanks.
Regards,
Xiaoguang Wang
Josef
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