On Thu, Oct 12, 2023 at 08:12:09PM -0700, Darrick J. Wong wrote: > I frankly have been asking myself why /this/ patchset adds so much extra > code and flags and whatnot to XFS and fs/verity. From what I can tell, > the xfs buffer cache has been extended to allocate double the memory so > that xattr contents can be shadowed. getxattr for merkle tree contents > then pins the buffer, shadows the contents, and hands both back to the > caller (aka xfs_read_merkle_tree_block). The shadow memory is then > handed to fs/verity to do its magic; following that, fsverity releases > the reference and we can eventually drop the xfs_buf reference. > > But this seems way overcomplicated to me. ->read_merkle_tree_page hands > us a pgoff_t and a suggestion for page readahead, and wants us to return > an uptodate locked page, right? It does. That beeing said I really much prefer the block based interface from Andrey. It is a lot cleaner and without weird page cache internals, although it can still be implemented very nicely by file systems that store the tree in the page cache. > The only thing I can't quite figure out is how to get memory reclaim to > scan the extra address_space when it wants to try to reclaim pages. > That part ext4 and f2fs got for free because they stuffed the merkle > tree in the posteof space. Except for th magic swapper_spaces, and address_space without an inode is not a thing, so you need to allocate an extra inode anyway, which is what reclaim works on.
