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

[Lance Yang <lance.yang@linux.dev>]

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@arm.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 is too verbose, how about 
SCAN_PAGE_DIRTY_WB?

It keeps the specificity without the length, and is arguably more 
descriptive
than NOT_CLEAN ;)

That said, LGTM.

Reviewed-by: Lance Yang <lance.yang@linux.dev>

> 
> SCAN_PAGE_NOT_CLEAN covers both states that indicate the page is not in a clean/stable
> state suitable for collapse.
> 
> [1] https://www.kernel.org/doc/Documentation/filesystems/proc.txt
> 
> Thanks,
> Shivank