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Date: Tue, 6 Aug 2024 12:17:47 +0100
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Subject: Re: [PATCH v1 07/11] mm/huge_memory: convert split_huge_pages_pid()
 from follow_page() to folio_walk
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To: David Hildenbrand <david@redhat.com>, linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org, linux-doc@vger.kernel.org, kvm@vger.kernel.org,
 linux-s390@vger.kernel.org, linux-fsdevel@vger.kernel.org,
 Andrew Morton <akpm@linux-foundation.org>,
 "Matthew Wilcox (Oracle)" <willy@infradead.org>,
 Jonathan Corbet <corbet@lwn.net>,
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 Janosch Frank <frankja@linux.ibm.com>,
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 <hca@linux.ibm.com>, Vasily Gorbik <gor@linux.ibm.com>,
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 Mark Brown <broonie@kernel.org>
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 <c75d1c6c-8ea6-424f-853c-1ccda6c77ba2@redhat.com>
From: Ryan Roberts <ryan.roberts@arm.com>
In-Reply-To: <c75d1c6c-8ea6-424f-853c-1ccda6c77ba2@redhat.com>
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>>>> 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 :)
>>
>> Ah, very likely the can_split_folio() check expects a raised refcount
>> already.
> 
> Indeed, the following does the trick! Thanks Ryan, I could have sworn
> I ran that selftest as well.

Ahha! Thanks for sorting so quickly!