On Tue 13-05-14 10:45:48, Mel Gorman wrote:
> Discarding buffers uses a bunch of atomic operations when discarding buffers
> because ...... I can't think of a reason. Use a cmpxchg loop to clear all the
> necessary flags. In most (all?) cases this will be a single atomic operations.
Looks good. You can add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
>
> Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
> ---
> fs/buffer.c | 14 +++++++++-----
> include/linux/buffer_head.h | 5 +++++
> 2 files changed, 14 insertions(+), 5 deletions(-)
>
> diff --git a/fs/buffer.c b/fs/buffer.c
> index 9ddb9fc..e80012d 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -1485,14 +1485,18 @@ EXPORT_SYMBOL(set_bh_page);
> */
> static void discard_buffer(struct buffer_head * bh)
> {
> + unsigned long b_state, b_state_old;
> +
> lock_buffer(bh);
> clear_buffer_dirty(bh);
> bh->b_bdev = NULL;
> - clear_buffer_mapped(bh);
> - clear_buffer_req(bh);
> - clear_buffer_new(bh);
> - clear_buffer_delay(bh);
> - clear_buffer_unwritten(bh);
> + b_state = bh->b_state;
> + for (;;) {
> + b_state_old = cmpxchg(&bh->b_state, b_state, (b_state & ~BUFFER_FLAGS_DISCARD));
> + if (b_state_old == b_state)
> + break;
> + b_state = b_state_old;
> + }
> unlock_buffer(bh);
> }
>
> diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
> index c40302f..95f565a 100644
> --- a/include/linux/buffer_head.h
> +++ b/include/linux/buffer_head.h
> @@ -77,6 +77,11 @@ struct buffer_head {
> atomic_t b_count; /* users using this buffer_head */
> };
>
> +/* Bits that are cleared during an invalidate */
> +#define BUFFER_FLAGS_DISCARD \
> + (1 << BH_Mapped | 1 << BH_New | 1 << BH_Req | \
> + 1 << BH_Delay | 1 << BH_Unwritten)
> +
> /*
> * macro tricks to expand the set_buffer_foo(), clear_buffer_foo()
> * and buffer_foo() functions.
> --
> 1.8.4.5
>
--
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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