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

From: Lance Yang

Date: Thu Nov 20 2025 - 07:24:59 EST



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@xxxxxxx>

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@xxxxxxxxx>


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