On 2021/4/16 上午3:27, Josef Bacik wrote:
On 4/15/21 1:04 AM, Qu Wenruo wrote:The new function, submit_eb_subpage(), will submit all the dirty extent buffers in the page. The major difference between submit_eb_page() and submit_eb_subpage() is: - How to grab extent buffer Now we use find_extent_buffer_nospinlock() other than using page::private. All other different handling is already done in functions like lock_extent_buffer_for_io() and write_one_eb(). Signed-off-by: Qu Wenruo <w...@suse.com> --- fs/btrfs/extent_io.c | 95 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 95 insertions(+) diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index c068c2fcba09..7d1fca9b87f0 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -4323,6 +4323,98 @@ static noinline_for_stack int write_one_eb(struct extent_buffer *eb, return ret; } +/* + * Submit one subpage btree page. + * + * The main difference between submit_eb_page() is: + * - Page locking + * For subpage, we don't rely on page locking at all. + * + * - Flush write bio + * We only flush bio if we may be unable to fit current extent buffers into + * current bio. + * + * Return >=0 for the number of submitted extent buffers. + * Return <0 for fatal error. + */ +static int submit_eb_subpage(struct page *page, + struct writeback_control *wbc, + struct extent_page_data *epd) +{ + struct btrfs_fs_info *fs_info = btrfs_sb(page->mapping->host->i_sb); + int submitted = 0; + u64 page_start = page_offset(page); + int bit_start = 0; + int nbits = BTRFS_SUBPAGE_BITMAP_SIZE; + int sectors_per_node = fs_info->nodesize >> fs_info->sectorsize_bits; + int ret; + + /* Lock and write each dirty extent buffers in the range */ + while (bit_start < nbits) { + struct btrfs_subpage *subpage = (struct btrfs_subpage *)page->private; + struct extent_buffer *eb; + unsigned long flags; + u64 start; + + /* + * Take private lock to ensure the subpage won't be detached + * halfway. + */ + spin_lock(&page->mapping->private_lock); + if (!PagePrivate(page)) { + spin_unlock(&page->mapping->private_lock); + break; + } + spin_lock_irqsave(&subpage->lock, flags);writepages doesn't get called with irq context, so you can just do spin_lock_irq()/spin_unlock_irq().
But this spinlock is used in endio function. If we don't use irqsave variant here, won't an endio interruption call sneak in and screw up everything?
+ if (!((1 << bit_start) & subpage->dirty_bitmap)) {Can we make this a helper so it's more clear what's going on here? Thanks,
That makes sense. Thanks, Qu
Josef
