linux-kernel - Re: [PATCH v1 07/11] mm/huge_memory: convert split_huge_pages_pid() from follow_page() to folio

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Message-ID: <ac97ccdc-ee1e-4f07-8902-6360de80c2a0@redhat.com>
Date: Tue, 6 Aug 2024 11:56:18 +0200
From: David Hildenbrand <david@...hat.com>
To: Ryan Roberts <ryan.roberts@....com>, linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org, linux-doc@...r.kernel.org, kvm@...r.kernel.org,
 linux-s390@...r.kernel.org, linux-fsdevel@...r.kernel.org,
 Andrew Morton <akpm@...ux-foundation.org>,
 "Matthew Wilcox (Oracle)" <willy@...radead.org>,
 Jonathan Corbet <corbet@....net>,
 Christian Borntraeger <borntraeger@...ux.ibm.com>,
 Janosch Frank <frankja@...ux.ibm.com>,
 Claudio Imbrenda <imbrenda@...ux.ibm.com>, Heiko Carstens
 <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
 Alexander Gordeev <agordeev@...ux.ibm.com>,
 Sven Schnelle <svens@...ux.ibm.com>,
 Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
 Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH v1 07/11] mm/huge_memory: convert split_huge_pages_pid()
 from follow_page() to folio_walk

On 06.08.24 11:46, Ryan Roberts wrote:
> On 02/08/2024 16:55, David Hildenbrand wrote:
>> Let's remove yet another follow_page() user. Note that we have to do the
>> split without holding the PTL, after folio_walk_end(). We don't care
>> about losing the secretmem check in follow_page().
> 
> Hi David,
> 
> Our (arm64) CI is showing a regression in split_huge_page_test from mm selftests from next-20240805 onwards. Navigating around a couple of other lurking bugs, I was able to bisect to this change (which smells about right).
> 
> Newly failing test:
> 
> # # ------------------------------
> # # running ./split_huge_page_test
> # # ------------------------------
> # # TAP version 13
> # # 1..12
> # # Bail out! Still AnonHugePages not split
> # # # Planned tests != run tests (12 != 0)
> # # # Totals: pass:0 fail:0 xfail:0 xpass:0 skip:0 error:0
> # # [FAIL]
> # not ok 52 split_huge_page_test # exit=1
> 
> It's trying to split some pmd-mapped THPs then checking and finding that they are not split. The split is requested via /sys/kernel/debug/split_huge_pages, which I believe ends up in this function you are modifying here. Although I'll admit that looking at the change, there is nothing obviously wrong! Any ideas?

Nothing jumps at me as well. Let me fire up the debugger :)

-- 
Cheers,

David / dhildenb