Re: [PATCH v3 2/2] ksm: Optimize rmap_walk_ksm by passing a suitable address range

[Lorenzo Stoakes]

On Tue, Apr 07, 2026 at 02:21:42PM -0700, Andrew Morton wrote:
> On Tue, 7 Apr 2026 10:43:12 +0100 "Lorenzo Stoakes (Oracle)" <ljs@xxxxxxxxxx> wrote:
>
> > > Thanks, Hugh.   Administreevia:
> > >
> > > I've removed this patch from the mm-stable branch and I reworked its
> > > [1/2] "ksm: initialize the addr only once in rmap_walk_ksm" to be
> > > presented as a singleton patch.
> > >
> > > For now I've restaged this patch ("ksm: optimize rmap_walk_ksm by
> > > passing a suitable address range") at the tail of the mm-unstable
> > > branch and I'll enter wait-and-see mode.
> > >
> >
> > Given we're at -rc7 now, I think we should delay this patch until 7.2, unless
> > I'm much mistaken wrt Hugh's concerns.
> >
> > I'm concerned this is a subtle way of breaking things so we really want to be
> > confident.
> >
> > We should also bundle up the test at
> > https://lore.kernel.org/all/20260407140805858ViqJKFhfmYSfq0FynsaEY@xxxxxxxxxx/
> > with this patch (should we find it's ok) as a separate series.
> >
> > Really overall I think safest to yank until 7.2 honestly.
>
> OK.  But let's not lose sight of those potential efficiency gains:
>
>          Time_ms      Nr_iteration_total    Skip_addr_out_of_range   Skip_mm_mismatch
> Before:  228.65       22169                 22168                    0
> After :   0.396        3                     0                       2
>

Yes, sure. We could possibly achieve similar by doing a quick search first then
trying the broader search as suggested by Hugh?

But want to make sure correctness is there!

Thanks, Lorenzo