On Thu, Jun 13, 2024 at 10:27:05PM -0700, Darrick J. Wong wrote: > > + * Unlike the data fork, the CoW cancellation functions will free all > > + * the reservations at inactivation, so we don't require that every > > + * delalloc reservation have a dirty pagecache. > > + * > > + * XXX(hch): I can't see where we actually require dirty pagecache > > + * for speculative data fork preallocations. What am I missing? > > IIRC a delalloc reservation in the data fork that isn't backing a dirty > page will just sit there in the data fork and never get reclaimed. > There's no writeback to turn it into an unwritten -> written extent. > The blockgc functions won't (can't?) walk the pagecache to find clean > regions that could be torn down. xfs destroy_inode just asserts on any > reservations that it finds. blockgc doesn't walk the page cache at all. It just calls xfs_free_eofblocks which simply drops all extents after i_size. If it didn't do that we'd be in trouble because there never is any dirty page cache past roundup(i_size, PAGE_SIZE).
