"Ritesh Harjani (IBM)" <ritesh.list@xxxxxxxxx> writes: ++ linux-ext4 > In continuation from last year's efforts on conversion of ext* filesystems to iomap, > I would like to propose an LSFMM session on the said topic. Last year's session > was mainly centered around documentation discussion around iomap (so that it can help others > converting their filesystems to iomap), and I think we now have a kernelnewbies page [1] > which can provide good details on how one can start transitioning their filesystem to iomap > interface. > > Note, ext2/ext4 filesystems direct-io path now utilizes iomap where ext2 > DIO conversion happened last year during LSFMM [2] [3]. I have also submitted patches > for ext2 buffered-io path for regular files to move to iomap and thereby enabling > large folio support to it. Along similar lines there are also patches around EXT4 > buffered-io conversion to iomap. > > Some of the challenges > ======================= > 1. For EXT2 directory handling which uses page cache and buffer heads, moving that path to > iomap has challenges with writeback path since iomap also uses folio->private to keep some > of its internal state (iomap_folio_state). > 2. One other thing which was pointed out by Matthew is the BH_Boundary handling currently missing > in iomap. This can lead to non-optimized data I/O patterns causing performance penalty. > 3. Filesystems need a mechanism to validate cached logical->physical block translations > in iomap writeback code (can this be lifted to common code?) > 4. Another missing piece from iomap is the metadata handling for filesystems. There is no > interface which iomap provides that the FS can utilize to move away from buffer heads > for its metadata operations. It can be argued that it is not the responsibility of iomap, however > filesystems do need a mechanism for their metadata handling operations. > > Proposal > ========= > In this talk I would like to discuss about the efforts, challenges & the lessons learnt in doing the conversion of > ext2's DIO and buffered-io paths to iomap, which might help others in conversion of their filesystem. > I would also like to have a discussion on the current open challenges we have in converting ext2 (buffered-io path) > and discuss on what ideas people have, which we can consider for transitioning ext* and other filesystems to iomap. > > PS: As we speak, I am in the process of rebasing ext2 bufferred-io path to latest upstream kernel. > It's mostly done and I am also looking into some of the open problems listed by community. > > > References > ============ > [1]: https://kernelnewbies.org/KernelProjects/iomap > [2]: https://lore.kernel.org/linux-ext4/cover.1682069716.git.ritesh.list@xxxxxxxxx/ > [3]: https://lwn.net/Articles/935934/ > [4]: https://lore.kernel.org/linux-ext4/cover.1700505907.git.ritesh.list@xxxxxxxxx/
