Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Michael Ellerman <mpe@ellerman.id.au>
To:     Matthew Wilcox <willy@infradead.org>,
        Michal Hocko <mhocko@kernel.org>
Cc:     Anshuman Khandual <anshuman.khandual@arm.com>, linux-mm@kvack.org,
        akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
        linuxppc-dev@lists.ozlabs.org,
        linux-arm-kernel@lists.infradead.org, linux-sh@vger.kernel.org,
        kvmarm@lists.cs.columbia.edu, linux-riscv@lists.infradead.org,
        linux@armlinux.org.uk, catalin.marinas@arm.com,
        will.deacon@arm.com, tglx@linutronix.de, mingo@redhat.com,
        dave.hansen@linux.intel.com, peterz@infradead.org,
        christoffer.dall@arm.com, marc.zyngier@arm.com,
        kirill@shutemov.name, rppt@linux.vnet.ibm.com,
        ard.biesheuvel@linaro.org, mark.rutland@arm.com,
        steve.capper@arm.com, james.morse@arm.com, robin.murphy@arm.com,
        aneesh.kumar@linux.ibm.com, vbabka@suse.cz, shakeelb@google.com,
        rientjes@google.com, palmer@sifive.com, greentime@andestech.com
Subject: Re: [PATCH V2] mm: Introduce GFP_PGTABLE
In-Reply-To: <20190116123018.GF6310@bombadil.infradead.org>
References: <1547619692-7946-1-git-send-email-anshuman.khandual@arm.com> <20190116065703.GE24149@dhcp22.suse.cz> <20190116123018.GF6310@bombadil.infradead.org>
Date:   Thu, 17 Jan 2019 20:56:34 +1100
Message-ID: <87tvi74nfx.fsf@concordia.ellerman.id.au>
MIME-Version: 1.0
Content-Type: text/plain
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Matthew Wilcox <willy@infradead.org> writes:

> On Wed, Jan 16, 2019 at 07:57:03AM +0100, Michal Hocko wrote:
>> On Wed 16-01-19 11:51:32, 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.
>> 
>> I haven't reviewed the patch yet but I am wondering whether this is
>> really worth it without going all the way down to unify the common code
>> and remove much more code duplication. Or is this not possible for some
>> reason?
>
> Exactly what I suggested doing in response to v1.
>
> Also, the approach taken here is crazy.  x86 has a feature that no other
> architecture has bothered to implement yet -- accounting page tables
> to the process.

powerpc does __GFP_ACCOUNT for user page tables too. Shamelessly cribbed
from the x86 version of course :)

cheers