Date: Wed, 24 Apr 2024 16:12:30 +0800
From: Zhang Yi <yi.zhang@...weicloud.com>
To: linux-ext4@...r.kernel.org, tytso@....edu, jack@...e.cz
Cc: linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, adilger.kernel@...ger.ca,
 ritesh.list@...il.com, hch@...radead.org, djwong@...nel.org,
 david@...morbit.com, willy@...radead.org, zokeefe@...gle.com,
 yi.zhang@...wei.com, chengzhihao1@...wei.com, yukuai3@...wei.com,
 wangkefeng.wang@...wei.com
Subject: Re: [RESEND RFC PATCH v4 00/34] ext4: use iomap for regular file's
 buffered IO path and enable large folio

Hi Ted and Jan,

I'm almost done with the first phase of this iomap conversion for
regular file's buffered IO path, could you please take time to take
a look at this series, I'd appreciated if I could get some feedback
and comments before the next phase of development, or is there any
plan to merge this series?

Thanks,
Yi.

On 2024/4/10 22:29, Zhang Yi wrote:
> Hello!
> 
> This is the fourth version of RFC patch series that convert ext4 regular
> file's buffered IO path to iomap and enable large folio. I've rebased it
> on 6.9-rc3, it also **depends on my xfs/iomap fix series** which has
> been reviewed but not merged yet[1]. Compared to the third vesion, this
> iteration fixes an issue discovered in current ext4 code, and contains
> another two main changes, 1) add bigalloc support and 2) simplify the
> updating logic of reserved delalloc data block, both changes could be
> sent out as preliminary patch series, besides these, others are some
> small code cleanups, performance optimize and commit log improvements.
> Please take a look at this series and any comments are welcome.
> 
> This series supports ext4 with the default features and mount
> options(bigalloc is also supported), doesn't support non-extent(ext3),
> inline_data, dax, fs_verity, fs_crypt and data=journal mode, ext4 would
> fall back to buffer_head path automatically if you enabled those
> features or options. Although it has many limitations now, it can satisfy
> the requirements of most common cases and bring a significant performance
> benefit for large IOs.
> 
> The iomap path would be simpler than the buffer_head path to some extent,
> please note that there are 4 major differences:
> 1. Always allocate unwritten extent for new blocks, it means that it's
>    not controlled by dioread_nolock mount option.
> 2. Since 1, there is no risk of exposing stale data during the append
>    write, so we don't need to write back data before metadata, it's time
>    to drop 'data = ordered' mode automatically.
> 3. Since 2, we don't need to reserve journal credits and use reserved
>    handle for the extent status conversion during writeback.
> 4. We could postpone updating the i_disksize to the endio, it could
>    avoid exposing zero data during append write and instantaneous power
>    failure.
> 
> Series details:
> Patch 1-9: this is the part 2 preparation series, it fix a problem
> first, and makes ext4_insert_delayed_block() call path support inserting
> multiple delalloc blocks (also support bigalloc), finally make
> ext4_da_map_blocks() buffer_head unaware, I've send it out separately[2]
> and hope this could be merged first.
> 
> Patch 10-19: this is the part 3 prepartory changes(picked out from my
> metadata reservation series[3], these are not a strong dependency
> patches, but I'd suggested these could be merged before the iomap
> conversion). These patches moves ext4_da_update_reserve_space() to
> ext4_es_insert_extent(), and always set EXT4_GET_BLOCKS_DELALLOC_RESERVE
> when allocating delalloc blocks, no matter it's from delayed allocate or
> non-delayed allocate (fallocate) path, it makes delalloc extents always
> delonly. These can make delalloc reservation simpler and cleaner than
> before.
> 
> Patch 20-34: These patches are the main implements of the buffered IO
> iomap conversion, It first introduce a sequence counter for extent
> status tree, then add a new iomap aops for read, write, mmap, replace
> current buffered_head path. Finally, enable iomap path besides inline
> data, non-extent, dax, fs_verity, fs_crypt, defrag and data=journal
> mode, if user specify "buffered_iomap" mount option, also enable large
> folio. Please look at the following patch for details.
> 
> About Tests:
>  - Pass kvm-xfstests in auto mode, and the keep running stress tests and
>    fault injection tests.
>  - A performance tests below (tested on my version 3 series,
>    theoretically there won't be much difference in this version).
> 
>    Fio tests with psync on my machine with Intel Xeon Gold 6240 CPU
>    with 400GB system ram, 200GB ramdisk and 1TB nvme ssd disk.
> 
>    == buffer read ==
> 
>                   buffer head        iomap + large folio
>    type     bs    IOPS    BW(MiB/s)  IOPS    BW(MiB/s)
>    ----------------------------------------------------
>    hole     4K    565k    2206       811k    3167
>    hole     64K   45.1k   2820       78.1k   4879
>    hole     1M    2744    2744       4890    4891
>    ramdisk  4K    436k    1703       554k    2163
>    ramdisk  64K   29.6k   1848       44.0k   2747
>    ramdisk  1M    1994    1995       2809    2809
>    nvme     4K    306k    1196       324k    1267
>    nvme     64K   19.3k   1208       24.3k   1517
>    nvme     1M    1694    1694       2256    2256
> 
>    == buffer write ==
> 
>                                         buffer head  iomap + large folio
>    type   Overwrite Sync Writeback bs   IOPS   BW    IOPS   BW
>    ------------------------------------------------------------
>    cache    N       N    N         4K   395k   1544  415k   1621
>    cache    N       N    N         64K  30.8k  1928  80.1k  5005
>    cache    N       N    N         1M   1963   1963  5641   5642
>    cache    Y       N    N         4K   423k   1652  443k   1730
>    cache    Y       N    N         64K  33.0k  2063  80.8k  5051
>    cache    Y       N    N         1M   2103   2103  5588   5589
>    ramdisk  N       N    Y         4K   362k   1416  307k   1198
>    ramdisk  N       N    Y         64K  22.4k  1399  64.8k  4050
>    ramdisk  N       N    Y         1M   1670   1670  4559   4560
>    ramdisk  N       Y    N         4K   9830   38.4  13.5k  52.8
>    ramdisk  N       Y    N         64K  5834   365   10.1k  629
>    ramdisk  N       Y    N         1M   1011   1011  2064   2064
>    ramdisk  Y       N    Y         4K   397k   1550  409k   1598
>    ramdisk  Y       N    Y         64K  29.2k  1827  73.6k  4597
>    ramdisk  Y       N    Y         1M   1837   1837  4985   4985
>    ramdisk  Y       Y    N         4K   173k   675   182k   710
>    ramdisk  Y       Y    N         64K  17.7k  1109  33.7k  2105
>    ramdisk  Y       Y    N         1M   1128   1129  1790   1791
>    nvme     N       N    Y         4K   298k   1164  290k   1134
>    nvme     N       N    Y         64K  21.5k  1343  57.4k  3590
>    nvme     N       N    Y         1M   1308   1308  3664   3664
>    nvme     N       Y    N         4K   10.7k  41.8  12.0k  46.9
>    nvme     N       Y    N         64K  5962   373   8598   537
>    nvme     N       Y    N         1M   676    677   1417   1418
>    nvme     Y       N    Y         4K   366k   1430  373k   1456
>    nvme     Y       N    Y         64K  26.7k  1670  56.8k  3547
>    nvme     Y       N    Y         1M   1745   1746  3586   3586
>    nvme     Y       Y    N         4K   59.0k  230   61.2k  239
>    nvme     Y       Y    N         64K  13.0k  813   21.0k  1311
>    nvme     Y       Y    N         1M   683    683   1368   1369
>  
> TODO
>  - Keep on doing stress tests and fixing.
>  - Reserve enough space for delalloc metadata blocks and try to drop
>    ext4_nonda_switch().
>  - First support defrag and then support other more unsupported features
>    and mount options.
> 
> Changes since v3:
>  - Drop the part 1 prepartory patches which have been merged [4].
>  - Drop the two iomap patches since I've submitted separately [1].
>  - Fix an incorrect reserved delalloc blocks count and incorrect extent
>    status cache issue found on current ext4 code.
>  - Pick out part 2 prepartory patch series [2], it make
>    ext4_insert_delayed_block() call path support inserting multiple
>    delalloc blocks (also support bigalloc )and make ext4_da_map_blocks()
>    buffer_head unaware.
>  - Adjust and simplify the reserved delalloc blocks updating logic,
>    preparing for reserving meta data blocks for delalloc.
>  - Drop datasync dirty check in ext4_set_iomap() for buffered
>    read/write, improves the concurrent performance on small I/Os.
>  - Prevent always hold invalid_lock in page_cache_ra_order(), add
>    lockless check.
>  - Disable iomap path by default since it's experimental new, add a
>    mount option "buffered_iomap" to enable it.
>  - Some other minor fixes and change log improvements.
> Changes since v2:
>  - Update patch 1-6 to v3.
>  - iomap_zero and iomap_unshare don't need to update i_size and call
>    iomap_write_failed(), introduce a new helper iomap_write_end_simple()
>    to avoid doing that.
>  - Factor out ext4_[ext|ind]_map_blocks() parts from ext4_map_blocks(),
>    introduce a new helper ext4_iomap_map_one_extent() to allocate
>    delalloc blocks in writeback, which is always under i_data_sem in
>    write mode. This is done to prevent the writing back delalloc
>    extents become stale if it raced by truncate.
>  - Add a lock detection in mapping_clear_large_folios().
> Changes since v1:
>  - Introduce seq count for iomap buffered write and writeback to protect
>    races from extents changes, e.g. truncate, mwrite.
>  - Always allocate unwritten extents for new blocks, drop dioread_lock
>    mode, and make no distinctions between dioread_lock and
>    dioread_nolock.
>  - Don't add ditry data range to jinode, drop data=ordered mode, and
>    make no distinctions between data=ordered and data=writeback mode.
>  - Postpone updating i_disksize to endio.
>  - Allow splitting extents and use reserved space in endio.
>  - Instead of reimplement a new delayed mapping helper
>    ext4_iomap_da_map_blocks() for buffer write, try to reuse
>    ext4_da_map_blocks().
>  - Add support for disabling large folio on active inodes.
>  - Support online defragmentation, make file fall back to buffer_head
>    and disable large folio in ext4_move_extents().
>  - Move ext4_nonda_switch() in advance to prevent deadlock in mwrite.
>  - Add dirty_len and pos trace info to trace_iomap_writepage_map().
>  - Update patch 1-6 to v2.
> 
> [1] https://lore.kernel.org/linux-xfs/20240320110548.2200662-1-yi.zhang@huaweicloud.com/
> [2] https://lore.kernel.org/linux-ext4/20240410034203.2188357-1-yi.zhang@huaweicloud.com/
> [3] https://lore.kernel.org/linux-ext4/20230824092619.1327976-1-yi.zhang@huaweicloud.com/
> [4] https://lore.kernel.org/linux-ext4/20240105033018.1665752-1-yi.zhang@huaweicloud.com/
> 
> Thanks,
> Yi.
> 
> ---
> v3: https://lore.kernel.org/linux-ext4/20240127015825.1608160-1-yi.zhang@huaweicloud.com/
> v2: https://lore.kernel.org/linux-ext4/20240102123918.799062-1-yi.zhang@huaweicloud.com/
> v1: https://lore.kernel.org/linux-ext4/20231123125121.4064694-1-yi.zhang@huaweicloud.com/
> 
> Zhang Yi (34):
>   ext4: factor out a common helper to query extent map
>   ext4: check the extent status again before inserting delalloc block
>   ext4: trim delalloc extent
>   ext4: drop iblock parameter
>   ext4: make ext4_es_insert_delayed_block() insert multi-blocks
>   ext4: make ext4_da_reserve_space() reserve multi-clusters
>   ext4: factor out check for whether a cluster is allocated
>   ext4: make ext4_insert_delayed_block() insert multi-blocks
>   ext4: make ext4_da_map_blocks() buffer_head unaware
>   ext4: factor out ext4_map_create_blocks() to allocate new blocks
>   ext4: optimize the EXT4_GET_BLOCKS_DELALLOC_RESERVE flag set
>   ext4: don't set EXTENT_STATUS_DELAYED on allocated blocks
>   ext4: let __revise_pending() return newly inserted pendings
>   ext4: count removed reserved blocks for delalloc only extent entry
>   ext4: update delalloc data reserve spcae in ext4_es_insert_extent()
>   ext4: drop ext4_es_delayed_clu()
>   ext4: use ext4_map_query_blocks() in ext4_map_blocks()
>   ext4: drop ext4_es_is_delonly()
>   ext4: drop all delonly descriptions
>   ext4: use reserved metadata blocks when splitting extent on endio
>   ext4: introduce seq counter for the extent status entry
>   ext4: add a new iomap aops for regular file's buffered IO path
>   ext4: implement buffered read iomap path
>   ext4: implement buffered write iomap path
>   ext4: implement writeback iomap path
>   ext4: implement mmap iomap path
>   ext4: implement zero_range iomap path
>   ext4: writeback partial blocks before zeroing out range
>   ext4: fall back to buffer_head path for defrag
>   ext4: partial enable iomap for regular file's buffered IO path
>   filemap: support disable large folios on active inode
>   ext4: enable large folio for regular file with iomap buffered IO path
>   ext4: don't mark IOMAP_F_DIRTY for buffer write
>   ext4: add mount option for buffered IO iomap path
> 

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