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From: Michal Hocko <mhocko@kernel.org>
To: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: mark.rutland@arm.com, linux-sh@vger.kernel.org,
	peterz@infradead.org, catalin.marinas@arm.com,
	dave.hansen@linux.intel.com, will.deacon@arm.com,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	kvmarm@lists.cs.columbia.edu, mpe@ellerman.id.au,
	linux@armlinux.org.uk, mingo@redhat.com, vbabka@suse.cz,
	rientjes@google.com, marc.zyngier@arm.com,
	rppt@linux.vnet.ibm.com, shakeelb@google.com,
	kirill@shutemov.name, tglx@linutronix.de,
	linux-arm-kernel@lists.infradead.org, ard.biesheuvel@linaro.org,
	robin.murphy@arm.com, steve.capper@arm.com,
	christoffer.dall@arm.com, james.morse@arm.com,
	aneesh.kumar@linux.ibm.com, akpm@linux-foundation.org,
	linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH] mm: Introduce GFP_PGTABLE
Date: Mon, 14 Jan 2019 08:01:37 +0100
Message-ID: <20190114070137.GB21345@dhcp22.suse.cz> (raw)
In-Reply-To: <f9f333a5-5533-996a-dc8e-1ff1096c1d19@arm.com>

On Mon 14-01-19 09:30:55, Anshuman Khandual wrote:
> 
> 
> On 01/13/2019 11:05 PM, Michal Hocko wrote:
> > On Sat 12-01-19 15:56:38, 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.
> > 
> > I agree that some unification is due but GFP_PGTABLE is not something to
> > expose in generic gfp.h IMHO. It just risks an abuse. I would be looking
> 
> Why would you think that it risks an abuse ? It does not create new semantics
> of allocation in the buddy. Its just uses existing GFP_KERNEL allocation which
> is then getting zeroed out. The risks (if any) is exactly same as GFP_KERNEL.

Beucase my experience just tells me that people tend to use whatever
they find and name fits what they think they need.

> > at providing asm-generic implementation and reuse it to remove the code
> 
> Does that mean GFP_PGTABLE can be created but not in gfp.h but in some other
> memory related header file ?

I would just keep it close to its users. If that is a single arch
generic place then only better. But I suspect some arches have special
requirements.

> > duplication. But I haven't tried that to know that it will work out due
> > to small/subtle differences between arches.
> 
> IIUC from the allocation perspective GFP_ACCOUNT is the only thing which gets
> added with GFP_PGTABLE for user page table for memcg accounting purpose. There
> does not seem to be any other differences unless I am missing something.

It's been some time since I've checked the last time. Some arches were
using GPF_REPEAT (__GFP_RETRY_MAYFAIL) back then. I have removed most of
those but some were doing a higher order allocations so they probably
have stayed.
-- 
Michal Hocko
SUSE Labs

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Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-12 10:26 Anshuman Khandual
2019-01-12 12:12 ` Matthew Wilcox
2019-01-12 12:55   ` Anshuman Khandual
2019-01-12 13:49   ` Christophe Leroy
2019-01-12 15:49     ` Matthew Wilcox
2019-01-12 16:50       ` Shakeel Butt
2019-01-14  4:28       ` Anshuman Khandual
2019-01-12 16:48 ` Shakeel Butt
2019-01-14  4:14   ` Anshuman Khandual
2019-01-13 17:35 ` Michal Hocko
2019-01-14  4:00   ` Anshuman Khandual
2019-01-14  7:01     ` Michal Hocko [this message]
2019-01-15 14:11       ` Anshuman Khandual

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