Re: [PATCH mm-new v6 2/5] mm: khugepaged: refine scan progress number

[Vernon Yang <vernon2gm@gmail.com>]

On Fri, Feb 06, 2026 at 10:02:48AM +0100, David Hildenbrand (Arm) wrote:
> On 2/5/26 15:25, Dev Jain wrote:
> >
> > On 05/02/26 5:41 pm, David Hildenbrand (arm) wrote:
> > > On 2/5/26 07:08, Vernon Yang wrote:
> > > > On Thu, Feb 5, 2026 at 5:35 AM David Hildenbrand (arm)
> > > > <david@kernel.org> wrote:
> > > >
> > > > I guess, your meaning is "min(_pte - pte + 1, HPAGE_PMD_NR)", not max().
> > >
> > > Yes!
> > >
> > > >
> > > >
> > > > I'm also worried that the compiler can't optimize this since the body of
> > > > the loop is complex, as with Dev's opinion [1].
> > >
> > > Why do we even have to optimize this? :)
> > >
> > > Premature ... ? :)
> >
> >
> > I mean .... we don't, but the alternate is a one liner using max().
>
> I'm fine with the max(), but it still seems like adding complexity to
> optimize something that is nowhere prove to really be a problem.

Hi David, Dev,

I use "*cur_progress += 1" at the beginning of the loop, the compiler
optimize that. Assembly as follows:

60c1:	4d 29 ca        sub    %r9,%r10		// r10 is _pte, r9 is pte, r10 = _pte - pte
60c4:	b8 00 02 00 00  mov    $0x200,%eax	// eax = HPAGE_PMD_NR
60c9:	44 89 5c 24 10  mov    %r11d,0x10(%rsp)	//
60ce:	49 c1 fa 03     sar    $0x3,%r10	//
60d2:	49 83 c2 01     add    $0x1,%r10	// r10 += 1
60d6:	49 39 c2        cmp    %rax,%r10	// r10 = min(r10, eax)
60d9:	4c 0f 4f d0     cmovg  %rax,%r10	//
60dd:	44 89 55 00     mov    %r10d,0x0(%rbp)	// *cur_progress = r10

To make the code simpler, Let us use "*cur_progress += 1".

--
Thanks,
Vernon