linux-kernel - Re: [PATCH V3 1/2] mm/khugepaged: map dirty/writeback pages failures to EAGAIN

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Message-ID: <c91f8c76-ca5a-4e8c-84a4-1b91b150e202@linux.alibaba.com>
Date: Tue, 2 Dec 2025 15:56:40 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Shivank Garg <shivankg@....com>, Andrew Morton
 <akpm@...ux-foundation.org>, David Hildenbrand <david@...nel.org>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Zi Yan <ziy@...dia.com>, "Liam R . Howlett" <Liam.Howlett@...cle.com>,
 Nico Pache <npache@...hat.com>, Ryan Roberts <ryan.roberts@....com>,
 Dev Jain <dev.jain@....com>, Barry Song <baohua@...nel.org>,
 Lance Yang <lance.yang@...ux.dev>, Steven Rostedt <rostedt@...dmis.org>,
 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,
 Branden Moore <Branden.Moore@....com>
Subject: Re: [PATCH V3 1/2] mm/khugepaged: map dirty/writeback pages failures
 to EAGAIN

On 2025/12/2 02:56, Shivank Garg wrote:
> When collapse_file encounters dirty or writeback pages in file-backed
> mappings, it currently returns SCAN_FAIL which maps to -EINVAL. This is
> misleading as EINVAL suggests invalid arguments, whereas dirty/writeback
> pages represent transient conditions that may resolve on retry.
> 
> Introduce SCAN_PAGE_DIRTY_OR_WRITEBACK to cover both dirty and writeback
> states, mapping it to -EAGAIN. For MADV_COLLAPSE, this provides userspace
> with a clear signal that retry may succeed after writeback completes.
> For khugepaged, this is harmless as it will naturally revisit the range
> during periodic scans after async writeback completes.
> 
> Reported-by: Branden Moore <Branden.Moore@....com>
> Closes: https://lore.kernel.org/all/4e26fe5e-7374-467c-a333-9dd48f85d7cc@amd.com
> Fixes: 34488399fa08 ("mm/madvise: add file and shmem support to MADV_COLLAPSE")
> Reviewed-by: Dev Jain <dev.jain@....com>
> Reviewed-by: Lance Yang <lance.yang@...ux.dev>
> Signed-off-by: Shivank Garg <shivankg@....com>
> ---

LGTM.
Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>