Re: [PATCH v1 05/11] mm: convert VM_PFNMAP tracking to pfnmap_track() + pfnmap_untrack()

Suren Baghdasaryan
2025-04-28T19:57:17Z

On Mon, Apr 28, 2025 at 12:37 PM Lorenzo Stoakes
<lorenzo.stoakes@oracle.com> wrote:
>
> On Mon, Apr 28, 2025 at 07:23:18PM +0200, David Hildenbrand wrote:
> > On 28.04.25 18:24, Peter Xu wrote:
> > > On Mon, Apr 28, 2025 at 06:16:21PM +0200, David Hildenbrand wrote:
> > > > > Probably due to what config you have. E.g., when I'm looking mine it's
> > > > > much bigger and already consuming 256B, but it's because I enabled more
> > > > > things (userfaultfd, lockdep, etc.).
> > > >
> > > > Note that I enabled everything that you would expect on a production system
> > > > (incld. userfaultfd, mempolicy, per-vma locks), so I didn't enable lockep.
> > >
> > > I still doubt whether you at least enabled userfaultfd, e.g., your previous
> > > paste has:
> > >
> > > struct vm_userfaultfd_ctx vm_userfaultfd_ctx; /* 176 0 */
> > >
> > > Not something that matters.. but just in case you didn't use the expected
> > > config file you wanted to use..
> >
> > You're absolutely right. I only briefly rechecked for this purpose here on
> > my notebook, and only looked for the existence of members, not expecting
> > that we have confusing stuff like vm_userfaultfd_ctx.
> >
> > I checked again and the size stays at 192 with allyesconfig and then
> > disabling debug options.
>
> I think a reasonable case is everything on, except CONFIG_DEBUG_LOCK_ALLOC and I
> don't care about nommu.

I think it's safe to assume that production systems would disable
lockdep due to the performance overhead. At least that's what we do on
Android - enable it on development branches but disable in production.

>
> So:
>
> CONFIG_PER_VMA_LOCK
> CONFIG_SWAP
> CONFIG_MMU (exclude the nommu vm_region field)
> CONFIG_NUMA
> CONFIG_NUMA_BALANCING
> CONFIG_PER_VMA_LOCK
> CONFIG_ANON_VMA_NAME
> __HAVE_PFNMAP_TRACKING
>
> So to be clear - allyesconfig w/o debug gives us this yes? And we don't add a
> cache line? In which case all good :)
>
>
> >
> > --
> > Cheers,
> >
> > David / dhildenb
> >
>