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btrfs: subpage: make reader lock utilize bitmap
Currently btrfs_subpage utilizes its atomic member @reader to manage the reader counter. However it is only utilized to prevent the page to be released/unlocked when we still have reads underway. In that use case, we don't really allow multiple readers on the same subpage sector. So here we can introduce a new locked bitmap to represent exactly which subpage range is locked for read. In theory we can remove btrfs_subpage::reader as it's just the set bits of the new locked bitmap. But unfortunately bitmap doesn't provide such handy API yet, so we still keep the reader counter. Signed-off-by: Qu Wenruo <wqu@suse.com> Reviewed-by: David Sterba <dsterba@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
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@ -111,6 +111,9 @@ void btrfs_init_subpage_info(struct btrfs_subpage_info *subpage_info, u32 sector
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subpage_info->checked_offset = cur;
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cur += nr_bits;
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subpage_info->locked_offset = cur;
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cur += nr_bits;
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subpage_info->total_nr_bits = cur;
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}
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@ -237,28 +240,58 @@ static void btrfs_subpage_assert(const struct btrfs_fs_info *fs_info,
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start + len <= folio_pos(folio) + PAGE_SIZE);
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}
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#define subpage_calc_start_bit(fs_info, folio, name, start, len) \
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({ \
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unsigned int start_bit; \
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\
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btrfs_subpage_assert(fs_info, folio, start, len); \
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start_bit = offset_in_page(start) >> fs_info->sectorsize_bits; \
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start_bit += fs_info->subpage_info->name##_offset; \
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start_bit; \
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})
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void btrfs_subpage_start_reader(const struct btrfs_fs_info *fs_info,
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struct folio *folio, u64 start, u32 len)
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{
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struct btrfs_subpage *subpage = folio_get_private(folio);
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const int start_bit = subpage_calc_start_bit(fs_info, folio, locked, start, len);
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const int nbits = len >> fs_info->sectorsize_bits;
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unsigned long flags;
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btrfs_subpage_assert(fs_info, folio, start, len);
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spin_lock_irqsave(&subpage->lock, flags);
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/*
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* Even though it's just for reading the page, no one should have
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* locked the subpage range.
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*/
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ASSERT(bitmap_test_range_all_zero(subpage->bitmaps, start_bit, nbits));
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bitmap_set(subpage->bitmaps, start_bit, nbits);
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atomic_add(nbits, &subpage->readers);
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spin_unlock_irqrestore(&subpage->lock, flags);
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}
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void btrfs_subpage_end_reader(const struct btrfs_fs_info *fs_info,
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struct folio *folio, u64 start, u32 len)
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{
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struct btrfs_subpage *subpage = folio_get_private(folio);
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const int start_bit = subpage_calc_start_bit(fs_info, folio, locked, start, len);
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const int nbits = len >> fs_info->sectorsize_bits;
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unsigned long flags;
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bool is_data;
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bool last;
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btrfs_subpage_assert(fs_info, folio, start, len);
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is_data = is_data_inode(folio->mapping->host);
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spin_lock_irqsave(&subpage->lock, flags);
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/* The range should have already been locked. */
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ASSERT(bitmap_test_range_all_set(subpage->bitmaps, start_bit, nbits));
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ASSERT(atomic_read(&subpage->readers) >= nbits);
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bitmap_clear(subpage->bitmaps, start_bit, nbits);
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last = atomic_sub_and_test(nbits, &subpage->readers);
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/*
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@ -270,6 +303,7 @@ void btrfs_subpage_end_reader(const struct btrfs_fs_info *fs_info,
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*/
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if (is_data && last)
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folio_unlock(folio);
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spin_unlock_irqrestore(&subpage->lock, flags);
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}
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static void btrfs_subpage_clamp_range(struct folio *folio, u64 *start, u32 *len)
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@ -365,16 +399,6 @@ void btrfs_folio_end_writer_lock(const struct btrfs_fs_info *fs_info,
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folio_unlock(folio);
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}
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#define subpage_calc_start_bit(fs_info, folio, name, start, len) \
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({ \
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unsigned int start_bit; \
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\
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btrfs_subpage_assert(fs_info, folio, start, len); \
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start_bit = offset_in_page(start) >> fs_info->sectorsize_bits; \
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start_bit += fs_info->subpage_info->name##_offset; \
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start_bit; \
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})
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#define subpage_test_bitmap_all_set(fs_info, subpage, name) \
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bitmap_test_range_all_set(subpage->bitmaps, \
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fs_info->subpage_info->name##_offset, \
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@ -751,6 +775,7 @@ void __cold btrfs_subpage_dump_bitmap(const struct btrfs_fs_info *fs_info,
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GET_SUBPAGE_BITMAP(subpage, subpage_info, writeback, &writeback_bitmap);
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GET_SUBPAGE_BITMAP(subpage, subpage_info, ordered, &ordered_bitmap);
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GET_SUBPAGE_BITMAP(subpage, subpage_info, checked, &checked_bitmap);
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GET_SUBPAGE_BITMAP(subpage, subpage_info, locked, &checked_bitmap);
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spin_unlock_irqrestore(&subpage->lock, flags);
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dump_page(folio_page(folio, 0), "btrfs subpage dump");
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@ -33,7 +33,7 @@ struct btrfs_subpage_info {
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unsigned int total_nr_bits;
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/*
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* *_start indicates where the bitmap starts, the length is always
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* *_offset indicates where the bitmap starts, the length is always
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* @bitmap_size, which is calculated from PAGE_SIZE / sectorsize.
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*/
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unsigned int uptodate_offset;
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@ -41,6 +41,16 @@ struct btrfs_subpage_info {
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unsigned int writeback_offset;
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unsigned int ordered_offset;
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unsigned int checked_offset;
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/*
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* For locked bitmaps, normally it's subpage representation for folio
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* Locked flag, but metadata is different:
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*
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* - Metadata doesn't really lock the folio
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* It's just to prevent page::private get cleared before the last
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* end_page_read().
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*/
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unsigned int locked_offset;
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};
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/*
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