Re: [PATCH] mm: replace xa_get_order with xas_get_order where appropriate

[Baolin Wang <baolin.wang@linux.alibaba.com>]

On 2024/9/7 07:05, Shakeel Butt wrote:
> The tracing of invalidation and truncation operations on large files
> showed that xa_get_order() is among the top functions where kernel
> spends a lot of CPUs. xa_get_order() needs to traverse the tree to reach
> the right node for a given index and then extract the order of the
> entry. However it seems like at many places it is being called within an
> already happening tree traversal where there is no need to do another
> traversal. Just use xas_get_order() at those places.
> 
> Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>

LGTM. Thanks.
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>

> ---
>   mm/filemap.c | 6 +++---
>   mm/shmem.c   | 2 +-
>   2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 070dee9791a9..7e3412941a8d 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -2112,7 +2112,7 @@ unsigned find_lock_entries(struct address_space *mapping, pgoff_t *start,
>   			VM_BUG_ON_FOLIO(!folio_contains(folio, xas.xa_index),
>   					folio);
>   		} else {
> -			nr = 1 << xa_get_order(&mapping->i_pages, xas.xa_index);
> +			nr = 1 << xas_get_order(&xas);
>   			base = xas.xa_index & ~(nr - 1);
>   			/* Omit order>0 value which begins before the start */
>   			if (base < *start)
> @@ -3001,7 +3001,7 @@ static inline loff_t folio_seek_hole_data(struct xa_state *xas,
>   static inline size_t seek_folio_size(struct xa_state *xas, struct folio *folio)
>   {
>   	if (xa_is_value(folio))
> -		return PAGE_SIZE << xa_get_order(xas->xa, xas->xa_index);
> +		return PAGE_SIZE << xas_get_order(xas);
>   	return folio_size(folio);
>   }
>   
> @@ -4297,7 +4297,7 @@ static void filemap_cachestat(struct address_space *mapping,
>   		if (xas_retry(&xas, folio))
>   			continue;
>   
> -		order = xa_get_order(xas.xa, xas.xa_index);
> +		order = xas_get_order(&xas);
>   		nr_pages = 1 << order;
>   		folio_first_index = round_down(xas.xa_index, 1 << order);
>   		folio_last_index = folio_first_index + nr_pages - 1;
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 866d46d0c43d..4002c4f47d4d 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -893,7 +893,7 @@ unsigned long shmem_partial_swap_usage(struct address_space *mapping,
>   		if (xas_retry(&xas, page))
>   			continue;
>   		if (xa_is_value(page))
> -			swapped += 1 << xa_get_order(xas.xa, xas.xa_index);
> +			swapped += 1 << xas_get_order(&xas);
>   		if (xas.xa_index == max)
>   			break;
>   		if (need_resched()) {