linux-kernel - Re: [PATCH v2 06/10] mm: avoid using vma

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Message-ID: <51452bab-65ef-4924-8ca8-61536d2bc168@sirena.org.uk>
Date: Thu, 29 Aug 2024 20:46:28 +0100
From: Mark Brown <broonie@...nel.org>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Liam R . Howlett" <Liam.Howlett@...cle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Ryan Roberts <ryan.roberts@....com>,
	Aishwarya TCV <aishwarya.tcv@....com>, dev.jain@....com
Subject: Re: [PATCH v2 06/10] mm: avoid using vma_merge() for new VMAs

On Fri, Aug 23, 2024 at 09:07:01PM +0100, Lorenzo Stoakes wrote:
> Abstract vma_merge_new_vma() to use vma_merge_struct and rename the
> resultant function vma_merge_new_range() to be clear what the purpose of
> this function is - a new VMA is desired in the specified range, and we wish
> to see if it is possible to 'merge' surrounding VMAs into this range rather
> than having to allocate a new VMA.

This patch, which is in -next today with the fixup Lorenzo posted as
commit 8c9d0f8b1e9a42586, seems to be causing problems with the mremap
expand merge selftest.  The test has been failing for a few days.  It
unfortunately doesn't log anything about why it's upset:

# # ok 15 5MB mremap - Source 1MB-aligned, Dest 1MB-aligned with 40MB Preamble
# # not ok 16 mremap expand merge
# # ok 18 mremap mremap move within range

I identified this commit using a bisect which appears to converge fairly
smoothly, I didn't do any other analysis:

git bisect start
# status: waiting for both good and bad commits
# bad: [b18bbfc14a38b5234e09c2adcf713e38063a7e6e] Add linux-next specific files for 20240829
git bisect bad b18bbfc14a38b5234e09c2adcf713e38063a7e6e
# status: waiting for good commit(s), bad commit known
# good: [559a93afece952cb129a236febe5d1b8f7c79367] Merge branch 'for-linux-next-fixes' of https://gitlab.freedesktop.org/drm/misc/kernel.git
git bisect good 559a93afece952cb129a236febe5d1b8f7c79367
# bad: [47b9fb7c1f3efb63f2a5ed614385476856196527] Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/ath/ath.git
git bisect bad 47b9fb7c1f3efb63f2a5ed614385476856196527
# bad: [3582529887df7b4d397a05584ceb9d9944b54328] Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux.git
git bisect bad 3582529887df7b4d397a05584ceb9d9944b54328
# bad: [a97442baf3538d884696539023a068269c983182] Merge branch 'at91-next' of git://git.kernel.org/pub/scm/linux/kernel/git/at91/linux.git
git bisect bad a97442baf3538d884696539023a068269c983182
# bad: [9287e4adbc6ab8fa04d25eb82e097fed877a4642] mm: optimization on page allocation when CMA enabled
git bisect bad 9287e4adbc6ab8fa04d25eb82e097fed877a4642
# good: [becee36d72a57fd245033efdfd94cb54ac24472e] mm: swap: extend swap_shmem_alloc() to support batch SWAP_MAP_SHMEM flag setting
git bisect good becee36d72a57fd245033efdfd94cb54ac24472e
# good: [8939071cd2fdfd69f48631845613f5d841e0e97e] selftests-test_zswap-add-test-for-hierarchical-zswapwriteback-fix
git bisect good 8939071cd2fdfd69f48631845613f5d841e0e97e
# bad: [42c5d3ae23db3086624db99c52498d5843d3b88a] mm/damon/core-test: fix damon_test_ops_registration() for DAMON_VADDR unset case
git bisect bad 42c5d3ae23db3086624db99c52498d5843d3b88a
# good: [6abe8def9543d42a31fa6560410a1ab45b3e1917] mm/vma: drop incorrect comment from vms_gather_munmap_vmas()
git bisect good 6abe8def9543d42a31fa6560410a1ab45b3e1917
# bad: [bdf4d125288d2ac24a49f7f52d882261bed6e1e1] mm: vmalloc: refactor vm_area_alloc_pages() function
git bisect bad bdf4d125288d2ac24a49f7f52d882261bed6e1e1
# good: [5cc3d95b7d3a1cd7c09772d6b7aaa0371cc37236] mm: abstract vma_expand() to use vma_merge_struct
git bisect good 5cc3d95b7d3a1cd7c09772d6b7aaa0371cc37236
# bad: [042a3d61fddaff155b6595d8e47323f1e85aefb3] mm: make vma_prepare() and friends static and internal to vma.c
git bisect bad 042a3d61fddaff155b6595d8e47323f1e85aefb3
# bad: [b46446ab789bc2cfc3d18ddcc0e93fa533f6b479] mm: only advance iterator if prev exists
git bisect bad b46446ab789bc2cfc3d18ddcc0e93fa533f6b479
# bad: [8c9d0f8b1e9a4258676714557c8d69fbb85578ab] mm: avoid using vma_merge() for new VMAs
git bisect bad 8c9d0f8b1e9a4258676714557c8d69fbb85578ab
# first bad commit: [8c9d0f8b1e9a4258676714557c8d69fbb85578ab] mm: avoid using vma_merge() for new VMAs

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