On 4/15/21 7:28 PM, Qu Wenruo wrote:
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?
No, you use irqsave if the function can be called under irq. So in the endio
call you do irqsave. This function can't be called by an interrupt handler, so
just _irq() is fine because you just need to disable irq's. Thanks,
Josef
