Re: [PATCH] Btrfs: set keep_lock when necessary in btrfs_defrag_leaves

[Liu Bo]

On Thu, Apr 26, 2018 at 4:01 AM, David Sterba  wrote:
> On Wed, Apr 25, 2018 at 09:40:34AM +0800, Liu Bo wrote:
>> path->keep_lock is set but @path immediatley gets released, this sets
>> ->keep_lock only when it's necessary.
>
> Can you please write down more details for context? This mostly repeats
> what the code does, but not why. Thanks.

Urr, right, I missed the important piece.

->keep_lock may hold the locks of all nodes on the path instead of
only level=1 node and level=0 leaf.  As it's more likely that lock
content happens on tree root and higher nodes, we have to release as
less locks as possible.

Will update in v2.

thanks,
liubo

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Re: [PATCH] Btrfs: set keep_lock when necessary in btrfs_defrag_leaves

[David Sterba]

On Wed, Apr 25, 2018 at 09:40:34AM +0800, Liu Bo wrote:
> path->keep_lock is set but @path immediatley gets released, this sets
> ->keep_lock only when it's necessary.

Can you please write down more details for context? This mostly repeats
what the code does, but not why. Thanks.
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[PATCH] Btrfs: set keep_lock when necessary in btrfs_defrag_leaves

[Liu Bo]

path->keep_lock is set but @path immediatley gets released, this sets
->keep_lock only when it's necessary.

Signed-off-by: Liu Bo 
---
 fs/btrfs/tree-defrag.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/fs/btrfs/tree-defrag.c b/fs/btrfs/tree-defrag.c
index 3c0987ab587d..c12747904d4c 100644
--- a/fs/btrfs/tree-defrag.c
+++ b/fs/btrfs/tree-defrag.c
@@ -65,8 +65,6 @@ int btrfs_defrag_leaves(struct btrfs_trans_handle *trans,
memcpy(, >defrag_progress, sizeof(key));
}
 
-   path->keep_locks = 1;
-
ret = btrfs_search_forward(root, , path, BTRFS_OLDEST_GENERATION);
if (ret < 0)
goto out;
@@ -81,6 +79,7 @@ int btrfs_defrag_leaves(struct btrfs_trans_handle *trans,
 * a deadlock (attempting to write lock an already write locked leaf).
 */
path->lowest_level = 1;
+   path->keep_locks = 1;
wret = btrfs_search_slot(trans, root, , path, 0, 1);
 
if (wret < 0) {
-- 
1.8.3.1

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