Re: [PATCH 00/12] mm/collapse: separate a collapse from its callers

[Kiryl Shutsemau]

On Sat, Sep 05, 2026 at 05:23:42PM -0700, Andrew Morton wrote:
> > Behaviour
> > =========
> > 
> > Nothing here changes what gets collapsed.  Three things a reader should
> > not have to find in the diff:
> > 
> >  - Patch 5: khugepaged fills its policy once per scan pass, so the
> >    max_ptes_* limits and the defrag setting behind the allocation mask are
> >    sampled once per pass rather than once per table.  A table scanned early
> >    in a pass and one scanned late are then judged alike, where before a
> >    knob written mid-pass split them.
> > 
> >  - Patch 8: mm_khugepaged_scan_pmd fires before mm_collapse_huge_page
> >    rather than after it, the scan having returned before the collapse
> >    runs.  Its status field already reads SCAN_SUCCEED for an accepted
> >    table, so nothing changes there; what the collapse then made of the
> >    table is mm_collapse_huge_page's to report, per order.
> > 
> >  - Patch 10: which orders a table is scanned for is sampled once per VMA
> >    rather than once per table.  It cannot widen what a collapse does --
> >    the order is tested again under the lock the collapse retakes.
> 
> So is *any* functional change expected with this series?

No.

The three items here are so nobody has to find them in the diff, and
calling them behaviour changes is a stretch: a sysfs knob written
mid-pass takes effect on the next pass instead of the next table, and a
tracepoint fires a few lines earlier with the same arguments.


> I'm reluctant to merge an unreviewed v1, but this comes close!  I'll
> sit on it for a week or less, see what people say.  Please poke me
> if/when you think it's good for mm-new.

Zi and Baolin have already provided enough feedback to justify v2.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov