On Wed, Jul 2, 2025 at 10:57 AM Darrick J. Wong <djwong@xxxxxxxxxx> wrote: > > On Wed, Jul 02, 2025 at 10:55:09AM -0700, Darrick J. Wong wrote: > > On Mon, Jun 23, 2025 at 07:21:31PM -0700, Joanne Koong wrote: > > > Have buffered writes go through iomap. This has two advantages: > > > * granular large folio synchronous reads > > > * granular large folio dirty tracking > > > > > > If for example there is a 1 MB large folio and a write issued at pos 1 > > > to pos 1 MB - 2, only the head and tail pages will need to be read in > > > and marked uptodate instead of the entire folio needing to be read in. > > > Non-relevant trailing pages are also skipped (eg if for a 1 MB large > > > folio a write is issued at pos 1 to 4099, only the first two pages are > > > read in and the ones after that are skipped). > > > > > > iomap also has granular dirty tracking. This is useful in that when it > > > comes to writeback time, only the dirty portions of the large folio will > > > be written instead of having to write out the entire folio. For example > > > if there is a 1 MB large folio and only 2 bytes in it are dirty, only > > > the page for those dirty bytes get written out. Please note that > > > granular writeback is only done once fuse also uses iomap in writeback > > > (separate commit). > > > > > > .release_folio needs to be set to iomap_release_folio so that any > > > allocated iomap ifs structs get freed. > > > > What happens in the !iomap case, which can still happen for > > !writeback_cache filesystems? I don't think you can call > > iomap_release_folio, because iomap doesn't own folio->private in that > > case. AFAICS, there's otherwise no private data attached to the folio for fuse for the non-writeback paths, so I don't think this is an issue. ifs_free() would be a no-op. > > ...and I think the answer to that is that the !writeback_cache case > passes all file IO directly to the fuse server and never touches the > page cache at all? There's two !writeback_cache cases, direct io and writethrough. For writethrough, the file IO gets passed to the fuse server and it also gets written to the page cache. > > --D >
