linux-kernel - Re: [PATCH V2 2/2] mm/khugepaged: map dirty/writeback pages failures to EAGAIN

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Message-ID: <81e34d93-9031-4840-a0d0-56d488f3bc17@kernel.org>
Date: Thu, 20 Nov 2025 14:29:23 +0100
From: "David Hildenbrand (Red Hat)" <david@...nel.org>
To: Lance Yang <lance.yang@...ux.dev>, "Garg, Shivank" <shivankg@....com>,
 Dev Jain <dev.jain@....com>
Cc: Zi Yan <ziy@...dia.com>, Baolin Wang <baolin.wang@...ux.alibaba.com>,
 "Liam R . Howlett" <Liam.Howlett@...cle.com>, Nico Pache
 <npache@...hat.com>, Ryan Roberts <ryan.roberts@....com>,
 Barry Song <baohua@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>,
 Steven Rostedt <rostedt@...dmis.org>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Masami Hiramatsu <mhiramat@...nel.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Zach O'Keefe <zokeefe@...gle.com>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH V2 2/2] mm/khugepaged: map dirty/writeback pages failures
 to EAGAIN

On 11/20/25 13:24, Lance Yang wrote:
> 
> 
> On 2025/11/20 16:17, Garg, Shivank wrote:
>>
>>
>> On 11/20/2025 1:33 PM, Dev Jain wrote:
>>>
>>> On 20/11/25 12:20 pm, Shivank Garg wrote:
>>
>>> SCAN_PAGE_NOT_CLEAN is confusing - NOT_CLEAN literally means dirty, so why not SCAN_PAGE_DIRTY?
>>> Or SCAN_PAGE_DIRTY_OR_UNDER_WRITEBACK? Since folio_test_writeback() is true as a result of
>>> the folio being dirty, maybe just SCAN_PAGE_DIRTY can do.
>>>
>>> Reviewed-by: Dev Jain <dev.jain@....com>
>>>
>> Thanks for the review.
>>
>> I chose not to use SCAN_PAGE_DIRTY because dirty and writeback have different meanings[1]:
>>
>>       Dirty: Memory that is waiting to be written back to disk
>> Writeback: Memory that is actively being written back to disk
>>
>> [1] https://www.kernel.org/doc/Documentation/filesystems/proc.txt
>>
>> IIUC, a page under writeback is no longer dirty, so using SCAN_PAGE_DIRTY would be misleading
>> for pages in the writeback state.
>>
>> I considered SCAN_PAGE_DIRTY_OR_WRITEBACK initially but felt it was too long.
> 
> Nit: If SCAN_PAGE_DIRTY_OR_WRITEBACK 

I would prefer that here.

-- 
Cheers

David