Re: [PATCH v2 09/18] btrfs: subpage: introduce helper for subpage uptodate status

[Nikolay Borisov <nborisov@suse.com>]

On 10.12.20 г. 8:38 ч., Qu Wenruo wrote:
> This patch introduce the following functions to handle btrfs subpage
> uptodate status:
> - btrfs_subpage_set_uptodate()
> - btrfs_subpage_clear_uptodate()
> - btrfs_subpage_test_uptodate()
>   Those helpers can only be called when the range is ensured to be
>   inside the page.
> 
> - btrfs_page_set_uptodate()
> - btrfs_page_clear_uptodate()
> - btrfs_page_test_uptodate()
>   Those helpers can handle both regular sector size and subpage without
>   problem.
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
>  fs/btrfs/subpage.h | 98 ++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 98 insertions(+)
> 
> diff --git a/fs/btrfs/subpage.h b/fs/btrfs/subpage.h
> index 87b4e028ae18..b3cf9171ec98 100644
> --- a/fs/btrfs/subpage.h
> +++ b/fs/btrfs/subpage.h
> @@ -23,6 +23,7 @@
>  struct btrfs_subpage {
>  	/* Common members for both data and metadata pages */
>  	spinlock_t lock;
> +	u16 uptodate_bitmap;
>  	union {
>  		/* Structures only used by metadata */
>  		struct {
> @@ -35,6 +36,17 @@ struct btrfs_subpage {
>  int btrfs_attach_subpage(struct btrfs_fs_info *fs_info, struct page *page);
>  void btrfs_detach_subpage(struct btrfs_fs_info *fs_info, struct page *page);
>  
> +static inline void btrfs_subpage_clamp_range(struct page *page,
> +					     u64 *start, u32 *len)
> +{
> +	u64 orig_start = *start;
> +	u32 orig_len = *len;
> +
> +	*start = max_t(u64, page_offset(page), orig_start);
> +	*len = min_t(u64, page_offset(page) + PAGE_SIZE,
> +		     orig_start + orig_len) - *start;
> +}

This handles EB's which span pages, right? If so - a comment is in order
since there is no design document specifying whether eb can or cannot
span multiple pages.

> +
>  /*
>   * Convert the [start, start + len) range into a u16 bitmap
>   *
> @@ -96,4 +108,90 @@ static inline bool btrfs_subpage_clear_and_test_tree_block(
>  	return last;
>  }
>  
> +static inline void btrfs_subpage_set_uptodate(struct btrfs_fs_info *fs_info,
> +			struct page *page, u64 start, u32 len)
> +{
> +	struct btrfs_subpage *subpage = (struct btrfs_subpage *)page->private;
> +	u16 tmp = btrfs_subpage_calc_bitmap(fs_info, page, start, len);
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&subpage->lock, flags);
> +	subpage->uptodate_bitmap |= tmp;
> +	if (subpage->uptodate_bitmap == (u16)-1)

just use U16_MAX instead of (u16)-1.

> +		SetPageUptodate(page);
> +	spin_unlock_irqrestore(&subpage->lock, flags);
> +}
> +
> +static inline void btrfs_subpage_clear_uptodate(struct btrfs_fs_info *fs_info,
> +			struct page *page, u64 start, u32 len)
> +{
> +	struct btrfs_subpage *subpage = (struct btrfs_subpage *)page->private;
> +	u16 tmp = btrfs_subpage_calc_bitmap(fs_info, page, start, len);
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&subpage->lock, flags);
> +	subpage->tree_block_bitmap &= ~tmp;

I  guess you meant to clear uptodate_bitmap and not tree_block_bitmap ?

> +	ClearPageUptodate(page);
> +	spin_unlock_irqrestore(&subpage->lock, flags);
> +}
> +

<snip>

> +DECLARE_BTRFS_SUBPAGE_TEST_OP(uptodate);
> +
> +/*
> + * Note that, in selftest, especially extent-io-tests, we can have empty
> + * fs_info passed in.
> + * Thanfully in selftest, we only test sectorsize == PAGE_SIZE cases so far

nit:s/Thankfully/Thankfully

> + * thus we can fall back to regular sectorsize branch.
> + */

<snip>

>