linux-kernel - Re: [PATCH] powerpc: add support for folded p4d page tables

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Message-ID: <20200106060217.GA5444@rapoport-lnx>
Date:   Mon, 6 Jan 2020 08:02:18 +0200
From:   Mike Rapoport <rppt@...nel.org>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        linuxppc-dev@...ts.ozlabs.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Mike Rapoport <rppt@...ux.ibm.com>
Subject: Re: [PATCH] powerpc: add support for folded p4d page tables

On Mon, Jan 06, 2020 at 02:31:41PM +1100, Michael Ellerman wrote:
> Mike Rapoport <rppt@...nel.org> writes:
> > Any updates on this?
> 
> It's very ... big, and kind of intrusive.

I've tried to split it to several smaller ones, but I couldn't find a way
to do it without breaking bisectability.

As for the intrusive, most of the changes are mechanical
 
> It's not an improvement as far as the powerpc code's readability is
> concerned. I assume the plan is that the 5-level hack can eventually be
> removed and so this conversion is a prerequisite for that?
 
Yep, the idea is to remove asm-generic/pgtable-nop4d-hack.h and
asm-generic/5level-fixup.h.

And, there is a small benefit for powerpc as kernel size is reduced a bit,
e.g. for pseries_defconfig:

$ size old/vmlinux new/vmlinux
   text	   data	    bss	    dec	    hex	filename
13702955	5961022	1517520	21181497	1433439  old/vmlinux
13702507	5961006	1517520	21181033	1433269  new/vmlinux

> cheers
> 
> > On Mon, Dec 09, 2019 at 05:09:08PM +0200, Mike Rapoport wrote:
> >> From: Mike Rapoport <rppt@...ux.ibm.com>
> >> 
> >> Implement primitives necessary for the 4th level folding, add walks of p4d
> >> level where appropriate and replace 5level-fixup.h with pgtable-nop4d.h.
> >> 
> >> Signed-off-by: Mike Rapoport <rppt@...ux.ibm.com>
> >> ---
> >>  arch/powerpc/include/asm/book3s/32/pgtable.h  |  1 -
> >>  arch/powerpc/include/asm/book3s/64/hash.h     |  4 +-
> >>  arch/powerpc/include/asm/book3s/64/pgalloc.h  |  4 +-
> >>  arch/powerpc/include/asm/book3s/64/pgtable.h  | 58 ++++++++++--------
> >>  arch/powerpc/include/asm/book3s/64/radix.h    |  6 +-
> >>  arch/powerpc/include/asm/nohash/32/pgtable.h  |  1 -
> >>  arch/powerpc/include/asm/nohash/64/pgalloc.h  |  2 +-
> >>  .../include/asm/nohash/64/pgtable-4k.h        | 32 +++++-----
> >>  arch/powerpc/include/asm/nohash/64/pgtable.h  |  6 +-
> >>  arch/powerpc/include/asm/pgtable.h            |  8 +++
> >>  arch/powerpc/kvm/book3s_64_mmu_radix.c        | 59 ++++++++++++++++---
> >>  arch/powerpc/lib/code-patching.c              |  7 ++-
> >>  arch/powerpc/mm/book3s32/mmu.c                |  2 +-
> >>  arch/powerpc/mm/book3s32/tlb.c                |  4 +-
> >>  arch/powerpc/mm/book3s64/hash_pgtable.c       |  4 +-
> >>  arch/powerpc/mm/book3s64/radix_pgtable.c      | 19 ++++--
> >>  arch/powerpc/mm/book3s64/subpage_prot.c       |  6 +-
> >>  arch/powerpc/mm/hugetlbpage.c                 | 28 +++++----
> >>  arch/powerpc/mm/kasan/kasan_init_32.c         |  8 +--
> >>  arch/powerpc/mm/mem.c                         |  4 +-
> >>  arch/powerpc/mm/nohash/40x.c                  |  4 +-
> >>  arch/powerpc/mm/nohash/book3e_pgtable.c       | 15 +++--
> >>  arch/powerpc/mm/pgtable.c                     | 25 +++++++-
> >>  arch/powerpc/mm/pgtable_32.c                  | 28 +++++----
> >>  arch/powerpc/mm/pgtable_64.c                  | 10 ++--
> >>  arch/powerpc/mm/ptdump/hashpagetable.c        | 20 ++++++-
> >>  arch/powerpc/mm/ptdump/ptdump.c               | 22 ++++++-
> >>  arch/powerpc/xmon/xmon.c                      | 17 +++++-
> >>  28 files changed, 284 insertions(+), 120 deletions(-)
> 

-- 
Sincerely yours,
Mike.