linux-kernel - Re: [PATCH V2] mm: Introduce GFP

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Date:   Wed, 16 Jan 2019 18:23:42 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Mike Rapoport <rppt@...ux.ibm.com>
Cc:     linux-mm@...ck.org, akpm@...ux-foundation.org,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-arm-kernel@...ts.infradead.org, linux-sh@...r.kernel.org,
        kvmarm@...ts.cs.columbia.edu, linux-riscv@...ts.infradead.org,
        linux@...linux.org.uk, catalin.marinas@....com,
        will.deacon@....com, mpe@...erman.id.au, tglx@...utronix.de,
        mingo@...hat.com, dave.hansen@...ux.intel.com,
        peterz@...radead.org, christoffer.dall@....com,
        marc.zyngier@....com, kirill@...temov.name,
        rppt@...ux.vnet.ibm.com, mhocko@...e.com,
        ard.biesheuvel@...aro.org, mark.rutland@....com,
        steve.capper@....com, james.morse@....com, robin.murphy@....com,
        aneesh.kumar@...ux.ibm.com, vbabka@...e.cz, shakeelb@...gle.com,
        rientjes@...gle.com, palmer@...ive.com, greentime@...estech.com
Subject: Re: [PATCH V2] mm: Introduce GFP_PGTABLE



On 01/16/2019 12:25 PM, Mike Rapoport wrote:
> On Wed, Jan 16, 2019 at 11:51:32AM +0530, Anshuman Khandual wrote:
>> All architectures have been defining their own PGALLOC_GFP as (GFP_KERNEL |
>> __GFP_ZERO) and using it for allocating page table pages. This causes some
>> code duplication which can be easily avoided. GFP_KERNEL allocated and
>> cleared out pages (__GFP_ZERO) are required for page tables on any given
>> architecture. This creates a new generic GFP flag flag which can be used
>> for any page table page allocation. Does not cause any functional change.
>>
>> GFP_PGTABLE is being added into include/asm-generic/pgtable.h which is the
>> generic page tabe header just to prevent it's potential misuse as a general
>> allocation flag if included in include/linux/gfp.h.
>>
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
>> ---
>> Build tested on arm, arm64, powerpc, powerpc64le and x86.
>> Boot tested on arm64 and x86.
>>
>> Changes in V2:
>>
>> - Moved GFP_PGTABLE into include/asm-generic/pgtable.h
>> - On X86 added __GFP_ACCOUNT into GFP_PGTABLE at various places
>> - Replaced possible flags on riscv and nds32 with GFP_PGTABLE
>>
>> Original V1: https://lkml.org/lkml/2019/1/12/54 
>>
>>  arch/arm/include/asm/pgalloc.h               |  8 +++-----
>>  arch/arm/mm/mmu.c                            |  2 +-
>>  arch/arm64/include/asm/pgalloc.h             |  9 ++++-----
>>  arch/arm64/mm/mmu.c                          |  2 +-
>>  arch/arm64/mm/pgd.c                          |  4 ++--
>>  arch/nds32/include/asm/pgalloc.h             |  3 +--
>>  arch/powerpc/include/asm/book3s/64/pgalloc.h |  6 +++---
>>  arch/powerpc/include/asm/pgalloc.h           |  2 --
>>  arch/powerpc/kvm/book3s_64_mmu_hv.c          |  2 +-
>>  arch/powerpc/mm/pgtable-frag.c               |  4 ++--
>>  arch/riscv/include/asm/pgalloc.h             |  8 +++-----
>>  arch/sh/mm/pgtable.c                         |  6 ++----
>>  arch/unicore32/include/asm/pgalloc.h         |  6 ++----
>>  arch/x86/kernel/espfix_64.c                  |  6 ++----
>>  arch/x86/mm/pgtable.c                        | 15 +++++++--------
>>  include/asm-generic/pgtable.h                |  2 ++
>>  virt/kvm/arm/mmu.c                           |  2 +-
>>  17 files changed, 37 insertions(+), 50 deletions(-)
> I wonder, what about the other arches? Do they use different GFP flags?
>  

Some of them as listed below use (GFP_KERNEL | __GFP_ZERO) which I will fix
next time around. Some how was focused on removing PGALLOC_GFP that missed
the other ones.

arch/powerpc/include/asm/nohash/64/pgalloc.h
arch/alpha/include/asm/pgalloc.h
arch/alpha/mm/init.c
arch/csky/include/asm/pgalloc.h
arch/arc/include/asm/pgalloc.h
........
........

But then there are those which use GFP_KERNEL alone without __GFP_ZERO like
pmd_alloc_one() in arch/sparc/include/asm/pgalloc_64.h cannot be replaced
with this patch as it does not intend to change functionality.