Ritesh Harjani (IBM) <ritesh.list@xxxxxxxxx> writes: > "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. I have rebased the RFC over the latest upstream and implemented the seq counter approach that was roughly discussed in the RFC patch here [1]. Please find the latest tree at my github [2], in case if anyone is interested in checking it out. Currently I am running some tests on this tree as we speak. Post that will look into BH_Boundary problem. [1]: https://lore.kernel.org/all/8734wnj53k.fsf@xxxxxxx/ [2]: https://github.com/riteshharjani/linux/commits/ext2-iomap-lsfmm-rfcv2/ -ritesh >> >> >> 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/
