Re: [RFC PATCH 01/12] khugepaged: Rename hpage_collapse_scan_pmd() -> ptes()

Zi Yan
2024-12-17T18:11:47Z

On 17 Dec 2024, at 1:43, Ryan Roberts wrote:

> On 17/12/2024 04:18, Matthew Wilcox wrote:
>> On Mon, Dec 16, 2024 at 10:20:54PM +0530, Dev Jain wrote:
>>> -static int hpage_collapse_scan_pmd(struct mm_struct *mm,
>>> +static int hpage_collapse_scan_ptes(struct mm_struct *mm,
>>
>> i don't think this is necessary at all. you're scanning a pmd.
>> you might not be scanning in order to collapse to a pmd, but pmd
>> is the level you're scanning at.
>>
>
> Sorry Matthew, I don't really understand this statement. Prior to the change we
> were scanning all PTE entries in a PTE table with the aim of collapsing to a PMD
> entry. After the change we are scanning some PTE entries in a PTE table with the
> aim of collapsing to either to a multi-PTE-mapped folio or a single-PMD-mapped
> folio.
>
> So personally I think "scan_pmd" was a misnomer even before the change - we are
> scanning the ptes.

But there are still a lot of scan_pmd code in the function, for example,
VM_BUG_ON(address & ~HPAGE_PMD_MASK), _pte < pte + HPAGE_PMD_NR in the function.
These need to be changed along with function renaming. If after the change only
a subset of PTEs are scanned within a PMD, maybe a scan_range parameter can be
added.

Best Regards,
Yan, Zi