在 2025/2/25 23:30, David Sterba 写道:
On Wed, Feb 12, 2025 at 01:22:45PM +1030, Qu Wenruo wrote:
Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
[...]
+ folio = filemap_get_folio(binode->vfs_inode.i_mapping,
+ cur >> PAGE_SHIFT);
Should this be folio_shift?
This is the biggest trap!
The filemap_* helpers are always using page index, no matter the folio size.
The filemap can be considered as a super large array of folio pointers.
(Implenmented by xarray)
For the current folio size == page size case, it's straight forward, if
there is a pointer then there is a cached folio for that index.
For larger folios, the overall idea is not changed, just we can have a
larger folio covering multiple slots, no longer one folio one slot.
So when doing the search we should always use PAGE_SHIFT.
And that why I hope the MM guys can provide a fileoff based
filemap_get_folio_by_fileoff().
CC MM guys, will a dedicated helper reduce such confusion?
Or it's just making the currently very simple filemap_*() helpers too
complex?
Thanks,
Qu
[...]
+again:
+ lock_extent(&binode->io_tree, start, end, cached_state);
+ cur_pos = start;
+ while (cur_pos < end) {
+ ordered = btrfs_lookup_ordered_range(binode, cur_pos,
+ end - cur_pos + 1);
+ /*
+ * No ordered extents in the range, and we hold the
+ * extent lock, no one can modify the extent maps
+ * in the range, we're safe to return.
+ */
+ if (!ordered)
+ break;
+
+ /* Check if we can skip waiting for the whole OE. */
+ if (can_skip_ordered_extent(binode, ordered, start, end)) {
+ cur_pos = min(ordered->file_offset + ordered->num_bytes,
+ end + 1);
+ btrfs_put_ordered_extent(ordered);
+ continue;
+ }
+
+ /* Now wait for the OE to finish. */
+ unlock_extent(&binode->io_tree, start, end,
+ cached_state);
+ btrfs_start_ordered_extent(ordered, start, end + 1 - start);
+ btrfs_put_ordered_extent(ordered);
+ /* We have unlocked the whole range, restart from the beginning. */
+ goto again;
This is a bit wild, goto at the end of a while loop but I don't see a
cleaner way without making complicated in another way.
I have fixed this in the one submitted the mail list, by introducing
another layer of while loop (in another function).
Thanks,
Qu
