btrfs: Refactor shrink_delalloc

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>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index d81035b7ea7d597e229975691fef48f8813a908a..0225659f2f42d5fdb496e396ee0f817a4fabfe95 100644 (file)
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -4741,7 +4741,7 @@ 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;
        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;
        u64 items;
        long time_left;
        unsigned long nr_pages;


@@ -4766,25 +4766,36 @@ static void shrink_delalloc(struct btrfs_fs_info *fs_info, u64 to_reclaim,
 
        loops = 0;
        while (delalloc_bytes && loops < 3) {
 
        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);
                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;
 
                        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
                else

-                       max_reclaim -= nr_pages;
+                       async_pages -= nr_pages;

 
                wait_event(fs_info->async_submit_wait,
                           atomic_read(&fs_info->async_delalloc_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) &&
 skip_async:
                spin_lock(&space_info->lock);
                if (list_empty(&space_info->tickets) &&