[PATCH 7/7] btrfs: Refactor shrink_delalloc

Nikolay Borisov
2019-01-03T08:50:15Z

Add a couple of comments regarding the logic flow in shrink_delalloc.
Then, cease using max_reclaim as a temporary variable when calculating
nr_pages. Finally give max_reclaim a more becoming name, which
uneqivocally shows at what this variable really holds. No functional
changes.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
---
fs/btrfs/extent-tree.c | 33 ++++++++++++++++++++++-----------
1 file changed, 22 insertions(+), 11 deletions(-)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index b15afeae16df..615441f4d458 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -4743,7 +4743,7 @@ static void shrink_delalloc(struct btrfs_fs_info *fs_info, u64 to_reclaim,
struct btrfs_space_info *space_info;
struct btrfs_trans_handle *trans;
u64 delalloc_bytes;
- u64 max_reclaim;
+ u64 async_pages;
u64 items;
long time_left;
unsigned long nr_pages;
@@ -4768,25 +4768,36 @@ static void shrink_delalloc(struct btrfs_fs_info *fs_info, u64 to_reclaim,

loops = 0;
while (delalloc_bytes && loops < 3) {
- max_reclaim = min(delalloc_bytes, to_reclaim);
- nr_pages = max_reclaim >> PAGE_SHIFT;
+ nr_pages = min(delalloc_bytes, to_reclaim) >> PAGE_SHIFT;
+
+ /*
+ * Triggers inode writeback for up to nr_pages. This will invoke
+ * ->writepages callback and trigger delalloc filling
+ * (btrfs_run_delalloc_range()).
+ */
btrfs_writeback_inodes_sb_nr(fs_info, nr_pages, items);
+
/*
- * We need to wait for the async pages to actually start before
- * we do anything.
+ * We need to wait for the compressed pages to start before
+ * we continue.
*/
- max_reclaim = atomic_read(&fs_info->async_delalloc_pages);
- if (!max_reclaim)
+ async_pages = atomic_read(&fs_info->async_delalloc_pages);
+ if (!async_pages)
goto skip_async;

- if (max_reclaim <= nr_pages)
- max_reclaim = 0;
+ /*
+ * Calculate how many compressed pages we want to be written
+ * before we continue. I.e if there are more async pages than we
+ * require wait_event will wait until nr_pages are written.
+ */
+ if (async_pages <= nr_pages)
+ async_pages = 0;
else
- max_reclaim -= nr_pages;
+ async_pages -= nr_pages;

wait_event(fs_info->async_submit_wait,
atomic_read(&fs_info->async_delalloc_pages) <=
- (int)max_reclaim);
+ (int)async_pages);
skip_async:
spin_lock(&space_info->lock);
if (list_empty(&space_info->tickets) &&
--
2.17.1