Date:   Wed, 30 Aug 2023 00:32:49 +0530
From:   Ritesh Harjani (IBM) <ritesh.list@...il.com>
To:     Kemeng Shi <shikemeng@...weicloud.com>, tytso@....edu,
        adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 00/11] cleanups and unit test for mballoc

Kemeng Shi <shikemeng@...weicloud.com> writes:

> v5-v6:
>

Hi Kemeng,

Sorry for the delay in getting started on this. I am going through the
series now.

> 1. Separate block bitmap and buddy bitmap freeing in individual patch
> and rewrite the descriptions.
> 2. Remove #ifdef around KUNIT_STATIC_STUB_REDIRECT which should be
> only defined when CONFIG_KUNIT is enabled after fix [7] which was merged
> into kunit-next/kunit
> 3. Use mbt prefix to distiguish test APIs from actual kernel APIs.
> 4. Add prepare function for ext4_mark_context and rename
> ext4_mb_mark_group_bb to ext4_mb_mark_context
> 5. Support to run mballoc test with different layouts setting and
> different block size is tested.
>
> v4->v5:
> 1. WARN on free blocks to uninitialized group is removed as normal
> fast commit route may triggers this, see [1] for details. The review
> tag from Ojaswin of changed patch is also removed and a futher review
> is needed.
>
> v3->v4:
> 1. Collect Reviewed-by from Ojaswin
> 2. Do improve as Ojaswin kindly suggested: Fix typo in commit,
> WARN if try to clear bit of uninitialized group and improve
> refactoring of AGGRESSIVE_CHECK code.
> 3. Fix conflic on patch 16
> 4. Improve git log in patch 16,17
>
> v2->v3:
> 1. Fix build warnings on "ext4: add some kunit stub for mballoc kunit
> test" and "ext4: add first unit test for ext4_mb_new_blocks_simple in
> mballoc"
>
> This series is a new version of unmerged patches from [1]. The first 6
> patches of this series factor out codes to mark blocks used or freed
> which will update on disk block bitmap and group descriptor. Several
> reasons to do this:
> 1. pair behavior of alloc/free bits. For example,
> ext4_mb_new_blocks_simple will update free_clusters in struct flex_groups
> in ext4_mb_mark_bb while ext4_free_blocks_simple forgets this.
> 2. remove repeat code to read from disk, update and write back to disk.
> 3. reduce future unit test mocks to avoid real IO to update structure
> on disk.
>
> The last 2 patches add a unit test for mballoc. Before more unit tests
> are added, there are something should be discussed:
> 1. How to test static function in mballoc.c
> Currently, include mballoc-test.c in mballoc.c to test static function
> in mballoc.c from mballoc-test.c which is one way suggested in [2].
> Not sure if there is any more elegant way to test static function without
> touch mballoc.c.
> 2. How to add mocks to function in mballoc.c which may issue IO to disk
> Currently, KUNIT_STATIC_STUB_REDIRECT is added to functions as suggested
> in kunit document [3].

I will get back to this, after reviwing some of the initial few
refactoring patches.

But FYI - I noticed some compilation errors, when building w/o
CONFIG_KUNIT.

../fs/ext4/balloc.c: In function ‘ext4_get_group_desc’:
../fs/ext4/balloc.c:278:2: error: implicit declaration of function ‘KUNIT_STATIC_STUB_REDIRECT’ [-Werror=implicit-function-declaration]
  278 |  KUNIT_STATIC_STUB_REDIRECT(ext4_get_group_desc,
      |  ^~~~~~~~~~~~~~~~~~~~~~~~~~

-ritesh

> 3. How to simulate a block bitmap.
> Currently, a fake buffer_head with bitmap data is returned, then no
> futher change is needed.
> If we simulate a block bitmap with an array of data structure like:
> struct test_bitmap {
>        unsigned int	start;
>        unsigned int	len;
> }
> which is suggested by Theodore in [4], then we need to add mocks to
> function which expected bitmap from bitmap_bh->b_data, like
> mb_find_next_bit, mb_find_next_zero_bit and maybe more.
>
> Would like to hear any suggestion! Thanks!
>
> I run kvm-xfstest with config "ext4/all" and "-g auto" together with
> patchset for resize, you can see detail report in [6].
>
> Unit test result is as followings:
> # ./tools/testing/kunit/kunit.py run --kunitconfig=fs/ext4/.kunitconfig --raw_output
> [18:23:36] Configuring KUnit Kernel ...
> [18:23:36] Building KUnit Kernel ...
> Populating config with:
> $ make ARCH=um O=.kunit olddefconfig
> Building with:
> $ make ARCH=um O=.kunit --jobs=88
> [18:23:40] Starting KUnit Kernel (1/1)...
> KTAP version 1
> 1..2
>     KTAP version 1
>     # Subtest: ext4_mballoc_test
>     1..1
>         KTAP version 1
>         # Subtest: test_new_blocks_simple
>         ok 1 block_bits=10 cluster_bits=3 blocks_per_group=8192 group_count=4 desc_size=64
>         ok 2 block_bits=12 cluster_bits=3 blocks_per_group=8192 group_count=4 desc_size=64
>         ok 3 block_bits=18 cluster_bits=3 blocks_per_group=8192 group_count=4 desc_size=64
>     # test_new_blocks_simple: pass:3 fail:0 skip:0 total:3
>     ok 1 test_new_blocks_simple
> # Totals: pass:3 fail:0 skip:0 total:3
> ok 1 ext4_mballoc_test
>     KTAP version 1
>     # Subtest: ext4_inode_test
>     1..1
>         KTAP version 1
>         # Subtest: inode_test_xtimestamp_decoding
>         ok 1 1901-12-13 Lower bound of 32bit < 0 timestamp, no extra bits
>         ok 2 1969-12-31 Upper bound of 32bit < 0 timestamp, no extra bits
>         ok 3 1970-01-01 Lower bound of 32bit >=0 timestamp, no extra bits
>         ok 4 2038-01-19 Upper bound of 32bit >=0 timestamp, no extra bits
>         ok 5 2038-01-19 Lower bound of 32bit <0 timestamp, lo extra sec bit on
>         ok 6 2106-02-07 Upper bound of 32bit <0 timestamp, lo extra sec bit on
>         ok 7 2106-02-07 Lower bound of 32bit >=0 timestamp, lo extra sec bit on
>         ok 8 2174-02-25 Upper bound of 32bit >=0 timestamp, lo extra sec bit on
>         ok 9 2174-02-25 Lower bound of 32bit <0 timestamp, hi extra sec bit on
>         ok 10 2242-03-16 Upper bound of 32bit <0 timestamp, hi extra sec bit on
>         ok 11 2242-03-16 Lower bound of 32bit >=0 timestamp, hi extra sec bit on
>         ok 12 2310-04-04 Upper bound of 32bit >=0 timestamp, hi extra sec bit on
>         ok 13 2310-04-04 Upper bound of 32bit>=0 timestamp, hi extra sec bit 1. 1 ns
>         ok 14 2378-04-22 Lower bound of 32bit>= timestamp. Extra sec bits 1. Max ns
>         ok 15 2378-04-22 Lower bound of 32bit >=0 timestamp. All extra sec bits on
>         ok 16 2446-05-10 Upper bound of 32bit >=0 timestamp. All extra sec bits on
>     # inode_test_xtimestamp_decoding: pass:16 fail:0 skip:0 total:16
>     ok 1 inode_test_xtimestamp_decoding
> # Totals: pass:16 fail:0 skip:0 total:16
> ok 2 ext4_inode_test
> [18:23:41] Elapsed time: 4.960s total, 0.001s configuring, 4.842s building, 0.072s running
>
> [1]
> https://lore.kernel.org/linux-ext4/20230603150327.3596033-1-shikemeng@huaweicloud.com/T/#m5ff8e3a058ce1cb272dfef3262cd3202ce6e4358
> [2]
> https://lore.kernel.org/linux-ext4/ZC3MoWn2UO6p+Swp@li-bb2b2a4c-3307-11b2-a85c-8fa5c3a69313.ibm.com/
> [3]
> https://docs.kernel.org/dev-tools/kunit/usage.html#testing-static-functions
> [4]
> https://docs.kernel.org/dev-tools/kunit/api/functionredirection.html#c.KUNIT_STATIC_STUB_REDIRECT
> [5]
> https://lore.kernel.org/linux-ext4/20230317155047.GB3270589@mit.edu/
> [6]
> https://lore.kernel.org/linux-ext4/20230629120044.1261968-1-shikemeng@huaweicloud.com/T/#mcc8fb0697fd54d9267c02c027e1eb3468026ae56
> [7]
> https://lore.kernel.org/lkml/20230725172051.2142641-1-shikemeng@huaweicloud.com/
>
> Kemeng Shi (11):
>   ext4: factor out codes to update block bitmap and group descriptor on
>     disk from ext4_mb_mark_bb
>   ext4: call ext4_mb_mark_context in ext4_free_blocks_simple
>   ext4: extent ext4_mb_mark_context to support allocation under journal
>   ext4: call ext4_mb_mark_context in ext4_mb_mark_diskspace_used
>   ext4: Separate block bitmap and buddy bitmap freeing in
>     ext4_mb_clear_bb()
>   ext4: call ext4_mb_mark_context in ext4_mb_clear_bb
>   ext4: Separate block bitmap and buddy bitmap freeing in
>     ext4_group_add_blocks()
>   ext4: call ext4_mb_mark_context in ext4_group_add_blocks()
>   ext4: add some kunit stub for mballoc kunit test
>   ext4: add first unit test for ext4_mb_new_blocks_simple in mballoc
>   ext4: run mballoc test with different layouts setting
>
>  fs/ext4/balloc.c       |  10 +
>  fs/ext4/mballoc-test.c | 351 ++++++++++++++++++++++++++++
>  fs/ext4/mballoc.c      | 505 ++++++++++++++++-------------------------
>  3 files changed, 557 insertions(+), 309 deletions(-)
>  create mode 100644 fs/ext4/mballoc-test.c
>
> -- 
> 2.30.0

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