Re: [PATCH v5 5/5] memblock: Disable mirror feature if kernelcore is not specified

[Baoquan He <bhe@redhat.com>]

On 06/14/22 at 12:27pm, Ard Biesheuvel wrote:
> On Tue, 14 Jun 2022 at 12:20, Baoquan He <bhe@redhat.com> wrote:
> >
> > On 06/14/22 at 05:21pm, Wupeng Ma wrote:
> > > From: Ma Wupeng <mawupeng1@huawei.com>
> > >
> > > If system have some mirrored memory and mirrored feature is not specified
> > > in boot parameter, the basic mirrored feature will be enabled and this will
> > > lead to the following situations:
> > >
> > > - memblock memory allocation prefers mirrored region. This may have some
> > >   unexpected influence on numa affinity.
> > >
> > > - contiguous memory will be split into several parts if parts of them
> > >   is mirrored memory via memblock_mark_mirror().
> > >
> > > To fix this, variable mirrored_kernelcore will be checked in
> > > memblock_mark_mirror(). Mark mirrored memory with flag MEMBLOCK_MIRROR iff
> > > kernelcore=mirror is added in the kernel parameters.
> > >
> > > Signed-off-by: Ma Wupeng <mawupeng1@huawei.com>
> > > Acked-by: Ard Biesheuvel <ardb@kernel.org>
> > > ---
> > >  mm/internal.h   | 2 ++
> > >  mm/memblock.c   | 3 +++
> > >  mm/page_alloc.c | 2 +-
> > >  3 files changed, 6 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/mm/internal.h b/mm/internal.h
> > > index c0f8fbe0445b..ddd2d6a46f1b 100644
> > > --- a/mm/internal.h
> > > +++ b/mm/internal.h
> > > @@ -861,4 +861,6 @@ struct folio *try_grab_folio(struct page *page, int refs, unsigned int flags);
> > >
> > >  DECLARE_PER_CPU(struct per_cpu_nodestat, boot_nodestats);
> > >
> > > +extern bool mirrored_kernelcore;
> > > +
> > >  #endif       /* __MM_INTERNAL_H */
> > > diff --git a/mm/memblock.c b/mm/memblock.c
> > > index b1d2a0009733..a9f18b988b7f 100644
> > > --- a/mm/memblock.c
> > > +++ b/mm/memblock.c
> > > @@ -924,6 +924,9 @@ int __init_memblock memblock_clear_hotplug(phys_addr_t base, phys_addr_t size)
> > >   */
> > >  int __init_memblock memblock_mark_mirror(phys_addr_t base, phys_addr_t size)
> > >  {
> > > +     if (!mirrored_kernelcore)
> > > +             return 0;
> >
> > memblock_mark_mirror() is just a wrapper, maybe we should check this in
> > efi_find_mirror(). Otherwise, how do we explain the message printed out
> > at below in boot log if we don't mark mirror memory at all?
> >
> > void __init efi_find_mirror(void)
> > {
> > ......
> >         if (mirror_size)
> >                 pr_info("Memory: %lldM/%lldM mirrored memory\n",
> >                         mirror_size>>20, total_size>>20);
> > }
> >
> 
> EFI does not care about *how* mirrored memory is being used or not, it
> just reports what the firmware provided. So EFI is not the appropriate
> level to take kernelcore=mirror into account.
> 
> I already mentioned that memblock_mark_mirror() is also the wrong
> place IMO, but Kefeng explained that doing it elsewhere is
> problematic.

OK, seems we have no better choice other than these two. 

>