ACK: [{groovy, focal}:linux-azure][PATCH] PM: hibernate: Batch hibernate and resume IO requests

[Kleber Souza]

On 11.12.20 20:52, Marcelo Henrique Cerri wrote:
> From: Xiaoyi Chen <cxiaoyi at amazon.com>
> 
> BugLink: https://bugs.launchpad.net/bugs/1904458
> 
> Hibernate and resume process submits individual IO requests for each page
> of the data, so use blk_plug to improve the batching of these requests.
> 
> Testing this change with hibernate and resumes consistently shows merging
> of the IO requests and more than an order of magnitude improvement in
> hibernate and resume speed is observed.
> 
> One hibernate and resume cycle for 16GB RAM out of 32GB in use takes
> around 21 minutes before the change, and 1 minutes after the change on
> a system with limited storage IOPS.
> 
> Signed-off-by: Xiaoyi Chen <cxiaoyi at amazon.com>
> Co-Developed-by: Anchal Agarwal <anchalag at amazon.com>
> Signed-off-by: Anchal Agarwal <anchalag at amazon.com>
> [ rjw: Subject and changelog edits, white space damage fixes ]
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
> (cherry picked from commit 55c4478a8f0ecedc0c1a0c9379380249985c372a)
> Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri at canonical.com>

Acked-by: Kleber Sacilotto de Souza <kleber.souza at canonical.com>

> ---
>   kernel/power/swap.c | 15 +++++++++++++++
>   1 file changed, 15 insertions(+)
> 
> diff --git a/kernel/power/swap.c b/kernel/power/swap.c
> index 01e2858b5fe3..116320a0394d 100644
> --- a/kernel/power/swap.c
> +++ b/kernel/power/swap.c
> @@ -226,6 +226,7 @@ struct hib_bio_batch {
>   	atomic_t		count;
>   	wait_queue_head_t	wait;
>   	blk_status_t		error;
> +	struct blk_plug		plug;
>   };
>   
>   static void hib_init_batch(struct hib_bio_batch *hb)
> @@ -233,6 +234,12 @@ static void hib_init_batch(struct hib_bio_batch *hb)
>   	atomic_set(&hb->count, 0);
>   	init_waitqueue_head(&hb->wait);
>   	hb->error = BLK_STS_OK;
> +	blk_start_plug(&hb->plug);
> +}
> +
> +static void hib_finish_batch(struct hib_bio_batch *hb)
> +{
> +	blk_finish_plug(&hb->plug);
>   }
>   
>   static void hib_end_io(struct bio *bio)
> @@ -294,6 +301,10 @@ static int hib_submit_io(int op, int op_flags, pgoff_t page_off, void *addr,
>   
>   static blk_status_t hib_wait_io(struct hib_bio_batch *hb)
>   {
> +	/*
> +	 * We are relying on the behavior of blk_plug that a thread with
> +	 * a plug will flush the plug list before sleeping.
> +	 */
>   	wait_event(hb->wait, atomic_read(&hb->count) == 0);
>   	return blk_status_to_errno(hb->error);
>   }
> @@ -561,6 +572,7 @@ static int save_image(struct swap_map_handle *handle,
>   		nr_pages++;
>   	}
>   	err2 = hib_wait_io(&hb);
> +	hib_finish_batch(&hb);
>   	stop = ktime_get();
>   	if (!ret)
>   		ret = err2;
> @@ -854,6 +866,7 @@ static int save_image_lzo(struct swap_map_handle *handle,
>   		pr_info("Image saving done\n");
>   	swsusp_show_speed(start, stop, nr_to_write, "Wrote");
>   out_clean:
> +	hib_finish_batch(&hb);
>   	if (crc) {
>   		if (crc->thr)
>   			kthread_stop(crc->thr);
> @@ -1084,6 +1097,7 @@ static int load_image(struct swap_map_handle *handle,
>   		nr_pages++;
>   	}
>   	err2 = hib_wait_io(&hb);
> +	hib_finish_batch(&hb);
>   	stop = ktime_get();
>   	if (!ret)
>   		ret = err2;
> @@ -1447,6 +1461,7 @@ static int load_image_lzo(struct swap_map_handle *handle,
>   	}
>   	swsusp_show_speed(start, stop, nr_to_read, "Read");
>   out_clean:
> +	hib_finish_batch(&hb);
>   	for (i = 0; i < ring_size; i++)
>   		free_page((unsigned long)page[i]);
>   	if (crc) {
>