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: <74536df6-98c7-43ac-9ae6-8106eea123ec@arm.com>
Date: Tue, 6 Aug 2024 12:17:47 +0100
From: Ryan Roberts <ryan.roberts@....com>
To: David Hildenbrand <david@...hat.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

>>>> 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!