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

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

On 2020/12/11 下午6:10, Nikolay Borisov wrote:
>
>
> 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.

Didn't I have already stated that in the subpage eb accessors patch?

No subpage eb can across page bounday.

>
>> +
>>  /*
>>   * 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 ?'

Oh my...

Thanks for catching this,
Qu
>
>> +	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>
>
>>