Re: [PATCH 7/7] btrfs: Refactor shrink_delalloc

David Sterba
2019-01-04T15:36:15Z

On Thu, Jan 03, 2019 at 10:50:05AM +0200, Nikolay Borisov wrote:
> 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;

This could be int, as it's compared to an atomic_t, otherwise ok.

> 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