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Message-ID: <bf6dcc97-a204-473c-9e25-54db430e9a58@huaweicloud.com>
Date: Tue, 22 Oct 2024 17:22:27 +0800
From: Zhang Yi <yi.zhang@...weicloud.com>
To: sedat.dilek@...il.com
Cc: linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
 linux-kernel@...r.kernel.org, tytso@....edu, adilger.kernel@...ger.ca,
 jack@...e.cz, ritesh.list@...il.com, hch@...radead.org, djwong@...nel.org,
 david@...morbit.com, zokeefe@...gle.com, yi.zhang@...wei.com,
 chengzhihao1@...wei.com, yukuai3@...wei.com, yangerkun@...wei.com
Subject: Re: [PATCH 00/27] ext4: use iomap for regular file's buffered I/O
 path and enable large folio

On 2024/10/22 14:59, Sedat Dilek wrote:
> On Tue, Oct 22, 2024 at 5:13 AM Zhang Yi <yi.zhang@...weicloud.com> wrote:
>>
>> From: Zhang Yi <yi.zhang@...wei.com>
>>
>> Hello!
>>
>> This patch series is the latest version based on my previous RFC
>> series[1], which converts the buffered I/O path of ext4 regular files to
>> iomap and enables large folios. After several months of work, almost all
>> preparatory changes have been upstreamed, thanks a lot for the review
>> and comments from Jan, Dave, Christoph, Darrick and Ritesh. Now it is
>> time for the main implementation of this conversion.
>>
>> This series is the main part of iomap buffered iomap conversion, it's
>> based on 6.12-rc4, and the code context is also depend on my anohter
>> cleanup series[1] (I've put that in this seris so we can merge it
>> directly), fixed all minor bugs found in my previous RFC v4 series.
>> Additionally, I've update change logs in each patch and also includes
>> some code modifications as Dave's suggestions. This series implements
>> the core iomap APIs on ext4 and introduces a mount option called
>> "buffered_iomap" to enable the iomap buffered I/O path. We have already
>> supported the default features, default mount options and bigalloc
>> feature. However, we do not yet support online defragmentation, inline
>> data, fs_verify, fs_crypt, ext3, and data=journal mode, ext4 will fall
>> to buffered_head I/O path automatically if you use those features and
>> options. Some of these features should be supported gradually in the
>> near future.
>>
>> Most of the implementations resemble the original buffered_head path;
>> however, there are four key differences.
>>
>> 1. The first aspect is the block allocation in the writeback path. The
>>    iomap frame will invoke ->map_blocks() at least once for each dirty
>>    folio. To ensure optimal writeback performance, we aim to allocate a
>>    range of delalloc blocks that is as long as possible within the
>>    writeback length for each invocation. In certain situations, we may
>>    allocate a range of blocks that exceeds the amount we will actually
>>    write back. Therefore,
>> 1) we cannot allocate a written extent for those blocks because it may
>>    expose stale data in such short write cases. Instead, we should
>>    allocate an unwritten extent, which means we must always enable the
>>    dioread_nolock option. This change could also bring many other
>>    benefits.
>> 2) We should postpone updating the 'i_disksize' until the end of the I/O
>>    process, based on the actual written length. This approach can also
>>    prevent the exposure of zero data, which may occur if there is a
>>    power failure during an append write.
>> 3) We do not need to pre-split extents during write-back, we can
>>    postpone this task until the end I/O process while converting
>>    unwritten extents.
>>
>> 2. The second reason is that since we always allocate unwritten space
>>    for new blocks, there is no risk of exposing stale data. As a result,
>>    we do not need to order the data, which allows us to disable the
>>    data=ordered mode. Consequently, we also do not require the reserved
>>    handle when converting the unwritten extent in the final I/O worker,
>>    we can directly start with the normal handle.
>>
>> Series details:
>>
>> Patch 1-10 is just another series of mine that refactors the fallocate
>> functions[1]. This series relies on the code context of that but has no
>> logical dependencies. I put this here just for easy access and merge.
>>
>> Patch 11-21 implement the iomap buffered read/write path, dirty folio
>> write back path and mmap path for ext4 regular file.
>>
>> Patch 22-23 disable the unsupported online-defragmentation function and
>> disable the changing of the inode journal flag to data=journal mode.
>> Please look at the following patch for details.
>>
>> Patch 24-27 introduce "buffered_iomap" mount option (is not enabled by
>> default now) to partially enable the iomap buffered I/O path and also
>> enable large folio.
>>
>>
>> About performance:
>>
>> Fio tests with psync on my machine with Intel Xeon Gold 6240 CPU with
>> 400GB system ram, 200GB ramdisk and 4TB nvme ssd disk.
>>
>>  fio -directory=/mnt -direct=0 -iodepth=$iodepth -fsync=$sync -rw=$rw \
>>      -numjobs=${numjobs} -bs=${bs} -ioengine=psync -size=$size \
>>      -runtime=60 -norandommap=0 -fallocate=none -overwrite=$overwrite \
>>      -group_reportin -name=$name --output=/tmp/test_log
>>
> 
> Hi Zhang Yi,
> 
> can you clarify about the FIO values for the diverse parameters?
> 

Hi Sedat,

Sure, the test I present here is a simple single-thread and single-I/O
depth case with psync ioengine. Most of the FIO parameters are shown
in the tables below.

For the rest, the 'iodepth' and 'numjobs' are always set to 1 and the
'size' is 40GB. During the write cache test, I also disable the write
back process through:

 echo 0 > /proc/sys/vm/dirty_writeback_centisecs
 echo 100 > /proc/sys/vm/dirty_background_ratio
 echo 100 > /proc/sys/vm/dirty_ratio

Thanks,
Yi.

> 
>>  == buffer read ==
>>
>>                 buffer_head        iomap + large folio
>>  type     bs    IOPS    BW(MiB/s)  IOPS    BW(MiB/s)
>>  -------------------------------------------------------
>>  hole     4K    576k    2253       762k    2975     +32%
>>  hole     64K   48.7k   3043       77.8k   4860     +60%
>>  hole     1M    2960    2960       4942    4942     +67%
>>  ramdisk  4K    443k    1732       530k    2069     +19%
>>  ramdisk  64K   34.5k   2156       45.6k   2850     +32%
>>  ramdisk  1M    2093    2093       2841    2841     +36%
>>  nvme     4K    339k    1323       364k    1425     +8%
>>  nvme     64K   23.6k   1471       25.2k   1574     +7%
>>  nvme     1M    2012    2012       2153    2153     +7%
>>
>>
>>  == buffer write ==
>>
>>                                        buffer_head  iomap + large folio
>>  type   Overwrite Sync Writeback  bs   IOPS   BW    IOPS   BW(MiB/s)
>>  ----------------------------------------------------------------------
>>  cache      N    N    N    4K     417k    1631    440k    1719   +5%
>>  cache      N    N    N    64K    33.4k   2088    81.5k   5092   +144%
>>  cache      N    N    N    1M     2143    2143    5716    5716   +167%
>>  cache      Y    N    N    4K     449k    1755    469k    1834   +5%
>>  cache      Y    N    N    64K    36.6k   2290    82.3k   5142   +125%
>>  cache      Y    N    N    1M     2352    2352    5577    5577   +137%
>>  ramdisk    N    N    Y    4K     365k    1424    354k    1384   -3%
>>  ramdisk    N    N    Y    64K    31.2k   1950    74.2k   4640   +138%
>>  ramdisk    N    N    Y    1M     1968    1968    5201    5201   +164%
>>  ramdisk    N    Y    N    4K     9984    39      12.9k   51     +29%
>>  ramdisk    N    Y    N    64K    5936    371     8960    560    +51%
>>  ramdisk    N    Y    N    1M     1050    1050    1835    1835   +75%
>>  ramdisk    Y    N    Y    4K     411k    1609    443k    1731   +8%
>>  ramdisk    Y    N    Y    64K    34.1k   2134    77.5k   4844   +127%
>>  ramdisk    Y    N    Y    1M     2248    2248    5372    5372   +139%
>>  ramdisk    Y    Y    N    4K     182k    711     186k    730    +3%
>>  ramdisk    Y    Y    N    64K    18.7k   1170    34.7k   2171   +86%
>>  ramdisk    Y    Y    N    1M     1229    1229    2269    2269   +85%
>>  nvme       N    N    Y    4K     373k    1458    387k    1512   +4%
>>  nvme       N    N    Y    64K    29.2k   1827    70.9k   4431   +143%
>>  nvme       N    N    Y    1M     1835    1835    4919    4919   +168%
>>  nvme       N    Y    N    4K     11.7k   46      11.7k   46      0%
>>  nvme       N    Y    N    64K    6453    403     8661    541    +34%
>>  nvme       N    Y    N    1M     649     649     1351    1351   +108%
>>  nvme       Y    N    Y    4K     372k    1456    433k    1693   +16%
>>  nvme       Y    N    Y    64K    33.0k   2064    74.7k   4669   +126%
>>  nvme       Y    N    Y    1M     2131    2131    5273    5273   +147%
>>  nvme       Y    Y    N    4K     56.7k   222     56.4k   220    -1%
>>  nvme       Y    Y    N    64K    13.4k   840     19.4k   1214   +45%
>>  nvme       Y    Y    N    1M     714     714     1504    1504   +111%
>>
>> Thanks,
>> Yi.
>>
>> Major changes since RFC v4:
>>  - Disable unsupported online defragmentation, do not fall back to
>>    buffer_head path.
>>  - Wite and wait data back while doing partial block truncate down to
>>    fix a stale data problem.
>>  - Disable the online changing of the inode journal flag to data=journal
>>    mode.
>>  - Since iomap can zero out dirty pages with unwritten extent, do not
>>    write data before zeroing out in ext4_zero_range(), and also do not
>>    zero partial blocks under a started journal handle.
>>
>> [1] https://lore.kernel.org/linux-ext4/20241010133333.146793-1-yi.zhang@huawei.com/
>>
>> ---
>> RFC v4: https://lore.kernel.org/linux-ext4/20240410142948.2817554-1-yi.zhang@huaweicloud.com/
>> RFC v3: https://lore.kernel.org/linux-ext4/20240127015825.1608160-1-yi.zhang@huaweicloud.com/
>> RFC v2: https://lore.kernel.org/linux-ext4/20240102123918.799062-1-yi.zhang@huaweicloud.com/
>> RFC v1: https://lore.kernel.org/linux-ext4/20231123125121.4064694-1-yi.zhang@huaweicloud.com/
>>
>>
>> Zhang Yi (27):
>>   ext4: remove writable userspace mappings before truncating page cache
>>   ext4: don't explicit update times in ext4_fallocate()
>>   ext4: don't write back data before punch hole in nojournal mode
>>   ext4: refactor ext4_punch_hole()
>>   ext4: refactor ext4_zero_range()
>>   ext4: refactor ext4_collapse_range()
>>   ext4: refactor ext4_insert_range()
>>   ext4: factor out ext4_do_fallocate()
>>   ext4: move out inode_lock into ext4_fallocate()
>>   ext4: move out common parts into ext4_fallocate()
>>   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: don't order data for inode with EXT4_STATE_BUFFERED_IOMAP
>>   ext4: implement writeback iomap path
>>   ext4: implement mmap iomap path
>>   ext4: do not always order data when partial zeroing out a block
>>   ext4: do not start handle if unnecessary while partial zeroing out a
>>     block
>>   ext4: implement zero_range iomap path
>>   ext4: disable online defrag when inode using iomap buffered I/O path
>>   ext4: disable inode journal mode when using iomap buffered I/O path
>>   ext4: partially enable iomap for the buffered I/O path of regular
>>     files
>>   ext4: enable large folio for regular file with iomap buffered I/O path
>>   ext4: change mount options code style
>>   ext4: introduce a mount option for iomap buffered I/O path
>>
>>  fs/ext4/ext4.h              |  17 +-
>>  fs/ext4/ext4_jbd2.c         |   3 +-
>>  fs/ext4/ext4_jbd2.h         |   8 +
>>  fs/ext4/extents.c           | 568 +++++++++++----------------
>>  fs/ext4/extents_status.c    |  13 +-
>>  fs/ext4/file.c              |  19 +-
>>  fs/ext4/ialloc.c            |   5 +
>>  fs/ext4/inode.c             | 755 ++++++++++++++++++++++++++++++------
>>  fs/ext4/move_extent.c       |   7 +
>>  fs/ext4/page-io.c           | 105 +++++
>>  fs/ext4/super.c             | 185 ++++-----
>>  include/trace/events/ext4.h |  57 +--
>>  12 files changed, 1153 insertions(+), 589 deletions(-)
>>
>> --
>> 2.46.1
>>
>>


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