leandrof/linux
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

btrfs: introduce write_one_subpage_eb() function

Browse Source 
The new function, write_one_subpage_eb(), as a subroutine for subpage
metadata write, will handle the extent buffer bio submission.

The major differences between the new write_one_subpage_eb() and
write_one_eb() is:

- No page locking
  When entering write_one_subpage_eb() the page is no longer locked.
  We only lock the page for its status update, and unlock immediately.
  Now we completely rely on extent io tree locking.

- Extra bitmap update along with page status update
  Now page dirty and writeback is controlled by
  btrfs_subpage::dirty_bitmap and btrfs_subpage::writeback_bitmap.
  They both follow the schema that any sector is dirty/writeback, then
  the full page gets dirty/writeback.

- When to update the nr_written number
  Now we take a shortcut, if we have cleared the last dirty bit of the
  page, we update nr_written.
  This is not completely perfect, but should emulate the old behavior
  well enough.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Qu Wenruo 2021-04-06 08:36:01 +08:00 committed by David Sterba
parent 2f3186d8ee
commit 35b6ddfa96
1 changed files with 53 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

53
fs/btrfs/extent_io.c
View File

@ -4197,6 +4197,56 @@ static void end_bio_extent_buffer_writepage(struct bio *bio)
bio_put(bio);
}
/*
* Unlike the work in write_one_eb(), we rely completely on extent locking.
* Page locking is only utilized at minimum to keep the VMM code happy.
*
* Caller should still call write_one_eb() other than this function directly.
* As write_one_eb() has extra preparation before submitting the extent buffer.
*/
static int write_one_subpage_eb(struct extent_buffer *eb,
struct writeback_control *wbc,
struct extent_page_data *epd)
{
struct btrfs_fs_info *fs_info = eb->fs_info;
struct page *page = eb->pages[0];
unsigned int write_flags = wbc_to_write_flags(wbc) | REQ_META;
bool no_dirty_ebs = false;
int ret;
/* clear_page_dirty_for_io() in subpage helper needs page locked */
lock_page(page);
btrfs_subpage_set_writeback(fs_info, page, eb->start, eb->len);
/* Check if this is the last dirty bit to update nr_written */
no_dirty_ebs = btrfs_subpage_clear_and_test_dirty(fs_info, page,
eb->start, eb->len);
if (no_dirty_ebs)
clear_page_dirty_for_io(page);
ret = submit_extent_page(REQ_OP_WRITE | write_flags, wbc, page,
eb->start, eb->len, eb->start - page_offset(page),
&epd->bio, end_bio_extent_buffer_writepage, 0, 0, 0,
false);
if (ret) {
btrfs_subpage_clear_writeback(fs_info, page, eb->start, eb->len);
set_btree_ioerr(page, eb);
unlock_page(page);
if (atomic_dec_and_test(&eb->io_pages))
end_extent_buffer_writeback(eb);
return -EIO;
}
unlock_page(page);
/*
* Submission finished without problem, if no range of the page is
* dirty anymore, we have submitted a page. Update nr_written in wbc.
*/
if (no_dirty_ebs)
update_nr_written(wbc, 1);
return ret;
}
static noinline_for_stack int write_one_eb(struct extent_buffer *eb,
struct writeback_control *wbc,
struct extent_page_data *epd)
@ -4228,6 +4278,9 @@ static noinline_for_stack int write_one_eb(struct extent_buffer *eb,
memzero_extent_buffer(eb, start, end - start);
}
if (eb->fs_info->sectorsize < PAGE_SIZE)
return write_one_subpage_eb(eb, wbc, epd);
for (i = 0; i < num_pages; i++) {
struct page *p = eb->pages[i];