From: Mike Rapoport <rppt@linux.ibm.com>
To: Marc Zyngier <maz@kernel.org>
Cc: Barry Song <song.bao.hua@hisilicon.com>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
Steve Capper <steve.capper@arm.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Wei Li <liwei213@huawei.com>,
butao@hisilicon.com, Will Deacon <will@kernel.org>,
Ard Biesheuvel <ardb@kernel.org>,
Nicolas Saenz Julienne <nsaenzjulienne@suse.de>,
fengbaopeng2@hisilicon.com
Subject: Re: [PATCH] arm64: mm: decrease the section size to reduce the memory reserved for the page map
Date: Mon, 7 Dec 2020 11:42:15 +0200 [thread overview]
Message-ID: <20201207094215.GC1112728@linux.ibm.com> (raw)
In-Reply-To: <390f5f441d99a832f4b2425b46f6d971@kernel.org>
On Mon, Dec 07, 2020 at 09:35:06AM +0000, Marc Zyngier wrote:
> On 2020-12-07 09:09, Ard Biesheuvel wrote:
> > (+ Marc)
> >
> > On Fri, 4 Dec 2020 at 12:14, Will Deacon <will@kernel.org> wrote:
> > >
> > > On Fri, Dec 04, 2020 at 09:44:43AM +0800, Wei Li wrote:
> > > > For the memory hole, sparse memory model that define SPARSEMEM_VMEMMAP
> > > > do not free the reserved memory for the page map, decrease the section
> > > > size can reduce the waste of reserved memory.
> > > >
> > > > Signed-off-by: Wei Li <liwei213@huawei.com>
> > > > Signed-off-by: Baopeng Feng <fengbaopeng2@hisilicon.com>
> > > > Signed-off-by: Xia Qing <saberlily.xia@hisilicon.com>
> > > > ---
> > > > arch/arm64/include/asm/sparsemem.h | 2 +-
> > > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/arch/arm64/include/asm/sparsemem.h b/arch/arm64/include/asm/sparsemem.h
> > > > index 1f43fcc79738..8963bd3def28 100644
> > > > --- a/arch/arm64/include/asm/sparsemem.h
> > > > +++ b/arch/arm64/include/asm/sparsemem.h
> > > > @@ -7,7 +7,7 @@
> > > >
> > > > #ifdef CONFIG_SPARSEMEM
> > > > #define MAX_PHYSMEM_BITS CONFIG_ARM64_PA_BITS
> > > > -#define SECTION_SIZE_BITS 30
> > > > +#define SECTION_SIZE_BITS 27
> > >
> > > We chose '30' to avoid running out of bits in the page flags. What
> > > changed?
> > >
> > > With this patch, I can trigger:
> > >
> > > ./include/linux/mmzone.h:1170:2: error: Allocator MAX_ORDER exceeds
> > > SECTION_SIZE
> > > #error Allocator MAX_ORDER exceeds SECTION_SIZE
> > >
> > > if I bump up NR_CPUS and NODES_SHIFT.
> > >
> >
> > Does this mean we will run into problems with the GICv3 ITS LPI tables
> > again if we are forced to reduce MAX_ORDER to fit inside
> > SECTION_SIZE_BITS?
>
> Most probably. We are already massively constraint on platforms
> such as TX1, and dividing the max allocatable range by 8 isn't
> going to make it work any better...
I don't think MAX_ORDER should shrink. Even if SECTION_SIZE_BITS is
reduced it should accomodate the existing MAX_ORDER.
My two pennies.
> M.
> --
> Jazz is not dead. It just smells funny...
--
Sincerely yours,
Mike.
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next prev parent reply other threads:[~2020-12-07 9:43 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-04 1:44 [PATCH] arm64: mm: decrease the section size to reduce the memory reserved for the page map Wei Li
2020-12-04 1:50 ` Song Bao Hua (Barry Song)
2020-12-04 11:13 ` Will Deacon
2020-12-04 11:44 ` Mike Rapoport
2020-12-07 1:40 ` Song Bao Hua (Barry Song)
2020-12-07 7:30 ` Anshuman Khandual
2020-12-07 7:47 ` Song Bao Hua (Barry Song)
2020-12-07 9:09 ` Ard Biesheuvel
2020-12-07 9:35 ` Marc Zyngier
2020-12-07 9:42 ` Mike Rapoport [this message]
2020-12-07 9:49 ` Ard Biesheuvel
2020-12-07 10:04 ` Mike Rapoport
2020-12-07 10:39 ` Anshuman Khandual
2020-12-07 12:07 ` Wei Li
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