Re: [PATCH v4 08/18] btrfs: introduce helper for subpage uptodate status

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

On 2021/1/20 下午11:00, Josef Bacik wrote:
> On 1/16/21 2:15 AM, 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.
>>    Although caller should still ensure that the range is inside the page.
>>
>> Signed-off-by: Qu Wenruo <wqu@suse.com>
>> ---
>>   fs/btrfs/subpage.h | 115 +++++++++++++++++++++++++++++++++++++++++++++
>>   1 file changed, 115 insertions(+)
>>
>> diff --git a/fs/btrfs/subpage.h b/fs/btrfs/subpage.h
>> index d8b34879368d..3373ef4ffec1 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 */
>>           bool under_alloc;
>> @@ -78,4 +79,118 @@ static inline void 
>> btrfs_page_end_meta_alloc(struct btrfs_fs_info *fs_info,
>>   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);
>> +/*
>> + * Convert the [start, start + len) range into a u16 bitmap
>> + *
>> + * E.g. if start == page_offset() + 16K, len = 16K, we get 0x00f0.
>> + */
>> +static inline u16 btrfs_subpage_calc_bitmap(struct btrfs_fs_info 
>> *fs_info,
>> +            struct page *page, u64 start, u32 len)
>> +{
>> +    int bit_start = offset_in_page(start) >> fs_info->sectorsize_bits;
>> +    int nbits = len >> fs_info->sectorsize_bits;
>> +
>> +    /* Basic checks */
>> +    ASSERT(PagePrivate(page) && page->private);
>> +    ASSERT(IS_ALIGNED(start, fs_info->sectorsize) &&
>> +           IS_ALIGNED(len, fs_info->sectorsize));
>> +
>> +    /*
>> +     * The range check only works for mapped page, we can
>> +     * still have unampped page like dummy extent buffer pages.
>> +     */
>> +    if (page->mapping)
>> +        ASSERT(page_offset(page) <= start &&
>> +            start + len <= page_offset(page) + PAGE_SIZE);
>> +    /*
>> +     * Here nbits can be 16, thus can go beyond u16 range. Here we 
>> make the
>> +     * first left shift to be calculated in unsigned long (u32), then
>> +     * truncate the result to u16.
>> +     */
>> +    return (u16)(((1UL << nbits) - 1) << bit_start);
>> +}
>> +
>> +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_MAX)
>> +        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->uptodate_bitmap &= ~tmp;
>> +    ClearPageUptodate(page);
>> +    spin_unlock_irqrestore(&subpage->lock, flags);
>> +}
>> +
>> +/*
>> + * Unlike set/clear which is dependent on each page status, for test 
>> all bits
>> + * are tested in the same way.
>> + */
>> +#define DECLARE_BTRFS_SUBPAGE_TEST_OP(name)                \
>> +static inline bool btrfs_subpage_test_##name(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;                        \
>> +    bool ret;                            \
>> +                                    \
>> +    spin_lock_irqsave(&subpage->lock, flags);            \
>> +    ret = ((subpage->name##_bitmap & tmp) == tmp);            \
>> +    spin_unlock_irqrestore(&subpage->lock, flags);            \
>> +    return ret;                            \
>> +}
>> +DECLARE_BTRFS_SUBPAGE_TEST_OP(uptodate);
>> +
>> +/*
>> + * Note that, in selftest, especially extent-io-tests, we can have empty
>> + * fs_info passed in.
>> + * Thankfully in selftest, we only test sectorsize == PAGE_SIZE cases 
>> so far,
>> + * thus we can fall back to regular sectorsize branch.
>> + */
>> +#define DECLARE_BTRFS_PAGE_OPS(name, set_page_func, 
>> clear_page_func,    \
>> +                   test_page_func)                \
>> +static inline void btrfs_page_set_##name(struct btrfs_fs_info 
>> *fs_info,    \
>> +            struct page *page, u64 start, u32 len)        \
>> +{                                    \
>> +    if (unlikely(!fs_info) || fs_info->sectorsize == PAGE_SIZE) {    \
>> +        set_page_func(page);                    \
>> +        return;                            \
>> +    }                                \
>> +    btrfs_subpage_set_##name(fs_info, page, start, len);        \
>> +}                                    \
>> +static inline void btrfs_page_clear_##name(struct btrfs_fs_info 
>> *fs_info, \
>> +            struct page *page, u64 start, u32 len)        \
>> +{                                    \
>> +    if (unlikely(!fs_info) || fs_info->sectorsize == PAGE_SIZE) {    \
>> +        clear_page_func(page);                    \
>> +        return;                            \
>> +    }                                \
>> +    btrfs_subpage_clear_##name(fs_info, page, start, len);        \
>> +}                                    \
>> +static inline bool btrfs_page_test_##name(struct btrfs_fs_info 
>> *fs_info, \
>> +            struct page *page, u64 start, u32 len)        \
>> +{                                    \
>> +    if (unlikely(!fs_info) || fs_info->sectorsize == PAGE_SIZE)    \
>> +        return test_page_func(page);                \
>> +    return btrfs_subpage_test_##name(fs_info, page, start, len);    \
>> +}
> 
> Another thing I just realized is you're doing this
> 
> btrfs_page_set_uptodate(fs_info, page, eb->start, eb->len);
> 
> but we default to a nodesize > PAGE_SIZE on x86.  This is fine, because 
> you're checking fs_info->sectorsize == PAGE_SIZE, which will mean we do 
> the right thing.
> 
> But what happens if fs_info->nodesize < PAGE_SIZE && fs_info->sectorsize 
> == PAGE_SIZE?  We by default have fs'es that ->nodesize != ->sectorsize, 
> so really what we should be doing is checking if len == PAGE_SIZE here, 
> but then you need to take into account the case that eb->len > 
> PAGE_SIZE.  Fix this to do the right thing in either of those cases.  
> Thanks,

Impossible.

Nodesize must be >= sectorsize.

As sectorsize is currently the minimal access unit for both data and 
metadata.

Thanks,
Qu

> 
> Josef