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Message-ID: <20240212061842.GB6180@frogsfrogsfrogs>
Date: Sun, 11 Feb 2024 22:18:42 -0800
From: "Darrick J. Wong" <djwong@...nel.org>
To: Zhang Yi <yi.zhang@...weicloud.com>
Cc: linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-mm@...ck.org, linux-kernel@...r.kernel.org, tytso@....edu,
adilger.kernel@...ger.ca, jack@...e.cz, ritesh.list@...il.com,
hch@...radead.org, willy@...radead.org, zokeefe@...gle.com,
yi.zhang@...wei.com, chengzhihao1@...wei.com, yukuai3@...wei.com,
wangkefeng.wang@...wei.com
Subject: Re: [RFC PATCH v3 00/26] ext4: use iomap for regular file's buffered
IO path and enable large foilo
On Sat, Jan 27, 2024 at 09:57:59AM +0800, Zhang Yi wrote:
> From: Zhang Yi <yi.zhang@...wei.com>
>
> Hello,
>
> This is the third version of RFC patch series that convert ext4 regular
> file's buffered IO path to iomap and enable large folio. It's rebased on
> 6.7 and Christoph's "map multiple blocks per ->map_blocks in iomap
> writeback" series [1]. I've fixed all issues found in the last about 3
> weeks of stress tests and fault injection tests in v2. I hope I've
> covered most of the corner cases, and any comments are welcome. :)
>
> Changes since v2:
> - Update patch 1-6 to v3 [2].
> - 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.
>
> This series only support ext4 with the default features and mount
> options, doesn't support inline_data, bigalloc, dax, fs_verity, fs_crypt
> and data=journal mode, ext4 would fall back to buffer_head path
Do you plan to add bigalloc or !extents support as a part 2 patchset?
An ext2 port to iomap has been (vaguely) in the works for a while,
though iirc willy never got the performance to match because iomap
didn't have a mechanism for the caller to tell it "run the IO now even
though you don't have a complete page, because the indirect block is the
next block after the 11th block".
--D
> automatically if you enabled these features/options. Although it has
> many limitations now, it can satisfy the requirements of common cases
> and bring a great performance benefit.
>
> Patch 1-6: this is a preparation series, it changes ext4_map_blocks()
> and ext4_set_iomap() to recognize delayed only extents, I've send it out
> separately [2].
>
> Patch 7-8: these are two minor iomap changes, the first one is don't
> update i_size and don't call iomap_write_failed() in zero_range, the
> second one is for debug in iomap writeback path that I've discussed whit
> Christoph [3].
>
> Patch 9-15: this is another preparation series, including some changes
> for delayed extents. Firstly, it factor out buffer_head from
> ext4_da_map_blocks(), make it to support adding multi-blocks once a
> time. Then make unwritten to written extents conversion in endio use to
> reserved space, reduce the risk of potential data loss. Finally,
> introduce a sequence counter for extent status tree, which is useful
> for iomap buffer write and write back.
>
> Patch 16-22: Implement buffered IO iomap path for read, write, mmap,
> zero range, truncate and writeback, replace current buffered_head path.
> Please look at the following patch for details.
>
> Patch 23-26: Convert to iomap for regular file's buffered IO path
> besides inline_data, bigalloc, dax, fs_verity, fs_crypt, and
> data=journal mode, and enable large folio. It should be note that
> buffered iomap path hasn't support Online defrag yet, so we need fall
> back to buffer_head and disable large folio automatically if user call
> EXT4_IOC_MOVE_EXT.
>
> About Tests:
> - kvm-xfstests in auto mode, and about 3 weeks of stress tests and
> fault injection tests.
> - A performance tests below.
>
> 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 with 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 ext4_iomap
> 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.
> - I will rebase and resend my another patch set "ext4: more accurate
> metadata reservaion for delalloc mount option[4]" later, it's useful
> for iomap conversion. After this series, I suppose we could totally
> drop ext4_nonda_switch() and prevent the risk of data loss caused by
> extents splitting.
> - Support for more features and mount options in the future.
>
> [1] https://lore.kernel.org/linux-fsdevel/20231207072710.176093-1-hch@lst.de/
> [2] https://lore.kernel.org/linux-ext4/20240105033018.1665752-1-yi.zhang@huaweicloud.com/
> [3] https://lore.kernel.org/linux-fsdevel/20231207150311.GA18830@lst.de/
> [4] https://lore.kernel.org/linux-ext4/20230824092619.1327976-1-yi.zhang@huaweicloud.com/
>
> Thanks,
> Yi.
>
> ---
> 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 (26):
> ext4: refactor ext4_da_map_blocks()
> ext4: convert to exclusive lock while inserting delalloc extents
> ext4: correct the hole length returned by ext4_map_blocks()
> ext4: add a hole extent entry in cache after punch
> ext4: make ext4_map_blocks() distinguish delalloc only extent
> ext4: make ext4_set_iomap() recognize IOMAP_DELALLOC map type
> iomap: don't increase i_size if it's not a write operation
> iomap: add pos and dirty_len into trace_iomap_writepage_map
> ext4: allow inserting delalloc extents with multi-blocks
> ext4: correct delalloc extent length
> ext4: also mark extent as delalloc if it's been unwritten
> ext4: factor out bh handles to ext4_da_get_block_prep()
> ext4: use reserved metadata blocks when splitting extent in endio
> ext4: factor out ext4_map_{create|query}_blocks()
> ext4: introduce seq counter for extent 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 zero range
> ext4: fall back to buffer_head path for defrag
> ext4: partially 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
>
> fs/ext4/ext4.h | 14 +-
> fs/ext4/ext4_jbd2.c | 6 +
> fs/ext4/ext4_jbd2.h | 7 +
> fs/ext4/extents.c | 149 +++---
> fs/ext4/extents_status.c | 39 +-
> fs/ext4/extents_status.h | 4 +-
> fs/ext4/file.c | 19 +-
> fs/ext4/ialloc.c | 5 +
> fs/ext4/inode.c | 891 +++++++++++++++++++++++++++---------
> fs/ext4/move_extent.c | 35 ++
> fs/ext4/page-io.c | 107 +++++
> fs/ext4/super.c | 3 +
> fs/iomap/buffered-io.c | 30 +-
> fs/iomap/trace.h | 43 +-
> include/linux/pagemap.h | 14 +
> include/trace/events/ext4.h | 31 +-
> mm/readahead.c | 6 +-
> 17 files changed, 1109 insertions(+), 294 deletions(-)
>
> --
> 2.39.2
>
>
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