linux-kernel - Re: [PATCH 3/6] null

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Date:   Wed, 5 Oct 2022 14:02:38 +0900
From:   Damien Le Moal <damien.lemoal@...nsource.wdc.com>
To:     Chaitanya Kulkarni <kch@...dia.com>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     axboe@...nel.dk, johannes.thumshirn@....com, bvanassche@....org,
        ming.lei@...hat.com, shinichiro.kawasaki@....com,
        vincent.fu@...sung.com, yukuai3@...wei.com
Subject: Re: [PATCH 3/6] null_blk: code cleaup

On 10/5/22 12:16, Chaitanya Kulkarni wrote:
> Introduce and use two new macros for calculating the page index from
> given sector and index (offset) of the sector in the page.
> The newly added macros makes code easy to read with meaningful name and
> explanation comments attached to it.
> 
> While at it adjust the code in the null_free_sector() to return early
> to get rid of the extra identation.
> 
> Signed-off-by: Chaitanya Kulkarni <kch@...dia.com>
> ---
>  drivers/block/null_blk/main.c | 37 ++++++++++++++++++++---------------
>  1 file changed, 21 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c
> index 2d592b4eb815..b82c2ffeb086 100644
> --- a/drivers/block/null_blk/main.c
> +++ b/drivers/block/null_blk/main.c
> @@ -14,6 +14,11 @@
>  #undef pr_fmt
>  #define pr_fmt(fmt)	"null_blk: " fmt
>  
> +/* Gives page index for which this sector belongs to. */

That is clear from the macro name. Not convinced this comment is useful.

> +#define PAGE_IDX_FROM_SECT(sect)	(sect >> PAGE_SECTORS_SHIFT)
> +/* Gives index (offset) of the sector within page. */
> +#define SECT_IDX_IN_PAGE(sect)		((sect & SECTOR_MASK) << SECTOR_SHIFT)

SECT_OFFSET_IN_PAGE() ? A "page" not being an array of sectors, using
index for a sector is a little strange I think. And you use this macro for
things like:

	offset = SECT_IDX_IN_PAGE(sect);

So offset in the name makes more sense.

> +
>  #define FREE_BATCH		16
>  
>  #define TICKS_PER_SEC		50ULL
> @@ -860,20 +865,20 @@ static void null_free_sector(struct nullb *nullb, sector_t sector,
>  	struct radix_tree_root *root;
>  
>  	root = is_cache ? &nullb->dev->cache : &nullb->dev->data;
> -	idx = sector >> PAGE_SECTORS_SHIFT;
> +	idx = PAGE_IDX_FROM_SECT(sector);
>  	sector_bit = (sector & SECTOR_MASK);
>  
>  	t_page = radix_tree_lookup(root, idx);
> -	if (t_page) {
> -		__clear_bit(sector_bit, t_page->bitmap);
> -
> -		if (null_page_empty(t_page)) {
> -			ret = radix_tree_delete_item(root, idx, t_page);
> -			WARN_ON(ret != t_page);
> -			null_free_page(ret);
> -			if (is_cache)
> -				nullb->dev->curr_cache -= PAGE_SIZE;
> -		}
> +	if (!t_page)
> +		return;
> +	__clear_bit(sector_bit, t_page->bitmap);
> +
> +	if (null_page_empty(t_page)) {
> +		ret = radix_tree_delete_item(root, idx, t_page);
> +		WARN_ON(ret != t_page);
> +		null_free_page(ret);
> +		if (is_cache)
> +			nullb->dev->curr_cache -= PAGE_SIZE;
>  	}
>  }
>  
> @@ -885,11 +890,11 @@ static void null_zero_sector(struct nullb_device *d, sector_t sect,
>  	unsigned int offset;
>  	void *dest;
>  
> -	t_page = radix_tree_lookup(root, sect >> PAGE_SECTORS_SHIFT);
> +	t_page = radix_tree_lookup(root, PAGE_IDX_FROM_SECT(sect));
>  	if (!t_page)
>  		return;
>  
> -	offset = (sect & SECTOR_MASK) << SECTOR_SHIFT;
> +	offset = SECT_IDX_IN_PAGE(sect);
>  	dest = kmap_atomic(t_page->page);
>  	memset(dest + offset, 0, SECTOR_SIZE * nr_sects);
>  	kunmap_atomic(dest);
> @@ -949,7 +954,7 @@ static struct nullb_page *__null_lookup_page(struct nullb *nullb,
>  	struct nullb_page *t_page;
>  	struct radix_tree_root *root;
>  
> -	idx = sector >> PAGE_SECTORS_SHIFT;
> +	idx = PAGE_IDX_FROM_SECT(sector);
>  	sector_bit = (sector & SECTOR_MASK);
>  
>  	root = is_cache ? &nullb->dev->cache : &nullb->dev->data;
> @@ -1125,7 +1130,7 @@ static int copy_to_nullb(struct nullb *nullb, struct page *source,
>  		if (null_cache_active(nullb) && !is_fua)
>  			null_make_cache_space(nullb, PAGE_SIZE);
>  
> -		offset = (sector & SECTOR_MASK) << SECTOR_SHIFT;
> +		offset = SECT_IDX_IN_PAGE(sector);
>  		t_page = null_insert_page(nullb, sector,
>  			!null_cache_active(nullb) || is_fua);
>  		if (!t_page)
> @@ -1159,7 +1164,7 @@ static int copy_from_nullb(struct nullb *nullb, struct page *dest,
>  	while (count < n) {
>  		temp = min_t(size_t, nullb->dev->blocksize, n - count);
>  
> -		offset = (sector & SECTOR_MASK) << SECTOR_SHIFT;
> +		offset = SECT_IDX_IN_PAGE(sector);
>  		t_page = null_lookup_page(nullb, sector, false,
>  			!null_cache_active(nullb));
>  

-- 
Damien Le Moal
Western Digital Research