[Devel] [RFC PATCH vz9 v6 22/62] dm-ploop: speed up ploop_prepare_bat_update()

[Pavel Tikhomirov]

On 12/6/24 05:55, Alexander Atanasov wrote:
> From: Andrey Zhadchenko <andrey.zhadchenko at virtuozzo.com>
> 
> Drop ploop_cluster_is_in_top_delta(), because
>   - it internally searches md on every call
>   - it takes read lock every time
> 
> https://virtuozzo.atlassian.net/browse/VSTOR-91817
> Signed-off-by: Andrey Zhadchenko <andrey.zhadchenko at virtuozzo.com>
> ---
>   drivers/md/dm-ploop-map.c | 15 +++++++++++----
>   1 file changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/md/dm-ploop-map.c b/drivers/md/dm-ploop-map.c
> index c89e28aa18f9..de885049e3f9 100644
> --- a/drivers/md/dm-ploop-map.c
> +++ b/drivers/md/dm-ploop-map.c
> @@ -899,13 +899,14 @@ static void ploop_bat_write_complete(struct pio *pio, void *piwb_ptr,
>   static int ploop_prepare_bat_update(struct ploop *ploop, struct md_page *md,
>   				    enum piwb_type type)
>   {
> -	u32 i, off, last, *bat_entries;
> +	u32 i, off, last, *bat_entries, clu;
>   	struct ploop_index_wb *piwb;
>   	bool is_last_page = true;
>   	u32 page_id = md->id;
>   	struct page *page;
>   	struct pio *pio;
>   	map_index_t *to;
> +	u8 level;
>   
>   	piwb = kmalloc(sizeof(*piwb), GFP_NOIO);
>   	if (!piwb)
> @@ -928,6 +929,8 @@ static int ploop_prepare_bat_update(struct ploop *ploop, struct md_page *md,
>   
>   	piwb->page_id = page_id;
>   	to = piwb->kmpage;
> +
> +	read_lock_irq(&md->lock);
>   	memcpy((void *)to, bat_entries, PAGE_SIZE);
>   
>   	/* Absolute number of first index in page (negative for page#0) */
> @@ -946,10 +949,14 @@ static int ploop_prepare_bat_update(struct ploop *ploop, struct md_page *md,
>   
>   	/* Copy BAT (BAT goes right after hdr, see .ctr) */
>   	for (; i < last; i++) {
> -		if (ploop_cluster_is_in_top_delta(ploop, i + off))
> -			continue;
> -		to[i] = 0;
> +		level = md->bat_levels[i];

Why do we assume that md page will not change when iterating from 
PLOOP_MAP_OFFSET and until (ploop->nr_bat_entries - (page_id * PAGE_SIZE 
/ sizeof(map_index_t) - PLOOP_MAP_OFFSET) ? If it's true, we need 
explanation in commit message. If false, we need to update md each time 
as ploop_cluster_is_in_top_delta did.

> +		clu = READ_ONCE(bat_entries[i]);
> +
> +		if (clu == BAT_ENTRY_NONE || level < ploop_top_level(ploop))
> +			to[i] = 0;
>   	}
> +	read_unlock_irq(&md->lock);
> +
>   	if (is_last_page) {
>   	/* Fill tail of page with 0 */
>   		for (i = last; i < PAGE_SIZE / sizeof(map_index_t); i++)

-- 
Best regards, Tikhomirov Pavel
Senior Software Developer, Virtuozzo.