Re: [PATCH mm-unstable v18 11/14] mm/khugepaged: Introduce mTHP collapse support

On 6/1/26 14:01, Nico Pache wrote:

On Sun, May 31, 2026 at 2:48 AM Lance Yang [off-list ref] wrote:

quoted

On 2026/5/31 15:18, Lance Yang wrote:

quoted

[...]

Hmm ... don't we lose the allocation-failure result here?

Previously collapse_scan_pmd() propagated SCAN_ALLOC_HUGE_PAGE_FAIL from
collapse_huge_page(), so khugepaged would call khugepaged_alloc_sleep()
in khugepaged_do_scan().

Now if allocation fails and nr_collapsed stays 0, we just return
SCAN_FAIL. So we won't back off via khugepaged_alloc_sleep() anymore?

Looks like this is a more general issue with mthp_collapse() only
returning nr_collapsed.

For example, SCAN_PMD_MAPPED used to be propagated too, and
madvise_collapse() treats that as success. With the new code, if
nothing was collapsed by this call, that can also become SCAN_FAIL ...

So I think we should keep both.

Yeah I thought about this before, but more regarding the "incorrect"
propagation of errors; I didn't consider that those results were
actually being considered.

I actually had a patch to track the last_failure (with some
prioritization on certain results). I think that would solve this
issue.

Thanks for reminding me to improve this.

Depending on how the rest of the reviews go, I can either send up a
follow up series to do some more cleanups and improvements of the
current approach or we can send out a v19.

Let's do a v19.

Patch #11 might need a bit of work, we can discuss offline if you want.

If we could get a v19 by the end of the week, that would be nice.

-- 
Cheers,

David