On Thu, Dec 03, 2015 at 05:56:32PM +0100, David Sterba wrote:
> The dellaloc work is not frequently used, the delayed status is once set
> and read so it looks quite safe to drop the member and store the status
> in the lowest bit of the inode pointer.
>
> Combined with the removal of 'wait' we got +2 objects per 4k slab.
>
> Signed-off-by: David Sterba <dsterba@xxxxxxxx>
> ---
> fs/btrfs/ctree.h | 5 ++++-
> fs/btrfs/inode.c | 11 +++++++++--
> 2 files changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index a61c53bce162..d5e250a65725 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -3901,8 +3901,11 @@ void btrfs_extent_item_to_extent_map(struct inode *inode,
>
> /* inode.c */
> struct btrfs_delalloc_work {
> + /*
> + * Note: lowest bit of inode tracks if the iput is delayed,
> + * do not access the pointer directly.
> + */
> struct inode *inode;
> - int delay_iput;
> struct completion completion;
> struct list_head list;
> struct btrfs_work work;
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index 15b29e879ffc..529a53b80ca0 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -9436,16 +9436,21 @@ static void btrfs_run_delalloc_work(struct btrfs_work *work)
> {
> struct btrfs_delalloc_work *delalloc_work;
> struct inode *inode;
> + int delay_iput;
>
> delalloc_work = container_of(work, struct btrfs_delalloc_work,
> work);
> inode = delalloc_work->inode;
> + /* Lowest bit of inode pointer tracks the delayed status */
> + delay_iput = ((unsigned long)inode & 1UL);
> + inode = (struct inode *)((unsigned long)inode & ~1UL);
> +
To be quite frankly, I don't like this, it's a pointer anyway, error-prone in a debugging view, instead would 'u8 delayed_iput' help?
Thanks,
-liubo
> filemap_flush(inode->i_mapping);
> if (test_bit(BTRFS_INODE_HAS_ASYNC_EXTENT,
> &BTRFS_I(inode)->runtime_flags))
> filemap_flush(inode->i_mapping);
>
> - if (delalloc_work->delay_iput)
> + if (delay_iput)
> btrfs_add_delayed_iput(inode);
> else
> iput(inode);
> @@ -9464,7 +9469,9 @@ struct btrfs_delalloc_work *btrfs_alloc_delalloc_work(struct inode *inode,
> init_completion(&work->completion);
> INIT_LIST_HEAD(&work->list);
> work->inode = inode;
> - work->delay_iput = delay_iput;
> + /* Lowest bit of inode pointer tracks the delayed status */
> + if (delay_iput)
> + *((unsigned long *)work->inode) |= 1UL;
> WARN_ON_ONCE(!inode);
> btrfs_init_work(&work->work, btrfs_flush_delalloc_helper,
> btrfs_run_delalloc_work, NULL, NULL);
> --
> 2.6.2
>
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