From: "Song Bao Hua (Barry Song)" <song.bao.hua@hisilicon.com>
To: Catalin Marinas <catalin.marinas@arm.com>,
Mike Rapoport <rppt@linux.ibm.com>,
"liwei (CM)" <liwei213@huawei.com>
Cc: "linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"steve.capper@arm.com" <steve.capper@arm.com>,
"Chenfeng \(puck\)" <puck.chen@hisilicon.com>,
sujunfei <sujunfei2@hisilicon.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Linuxarm <linuxarm@huawei.com>,
"Xiaqing \(A\)" <saberlily.xia@hisilicon.com>,
butao <butao@hisilicon.com>, "will@kernel.org" <will@kernel.org>,
"nsaenzjulienne@suse.de" <nsaenzjulienne@suse.de>,
fengbaopeng <fengbaopeng2@hisilicon.com>
Subject: RE: [PATCH v2] arm64: mm: free unused memmap for sparse memory model that define VMEMMAP
Date: Mon, 16 Nov 2020 08:33:43 +0000 [thread overview]
Message-ID: <eacfa2bb19df4126a476566512d93dab@hisilicon.com> (raw)
In-Reply-To: <20200903120558.GB31409@gaia>
> -----Original Message-----
> From: Catalin Marinas [mailto:catalin.marinas@arm.com]
> Sent: Friday, September 4, 2020 12:06 AM
> To: Mike Rapoport <rppt@linux.ibm.com>
> Cc: liwei (CM) <liwei213@huawei.com>; will@kernel.org; Xiaqing (A)
> <saberlily.xia@hisilicon.com>; Chenfeng (puck) <puck.chen@hisilicon.com>;
> butao <butao@hisilicon.com>; fengbaopeng <fengbaopeng2@hisilicon.com>;
> nsaenzjulienne@suse.de; steve.capper@arm.com; Song Bao Hua (Barry Song)
> <song.bao.hua@hisilicon.com>; linux-arm-kernel@lists.infradead.org;
> linux-kernel@vger.kernel.org; sujunfei <sujunfei2@hisilicon.com>
> Subject: Re: [PATCH v2] arm64: mm: free unused memmap for sparse memory
> model that define VMEMMAP
>
> On Mon, Aug 17, 2020 at 11:04:05AM +0300, Mike Rapoport wrote:
> > On Wed, Aug 12, 2020 at 09:06:55AM +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, this patch do it.
> >
> > I've been thinking about it a bit more and it seems that instead of
> > freeing unused memory map it would be better to allocate the exact
> > memory map from the beginning.
> >
> > In sparse_init_nid() we can replace PAGES_PER_SECTION parameter to
> > __populate_section_memmap() with the calculated value for architectures
> > that define HAVE_ARCH_PFN_VALID.
>
> Or just use a smaller PAGES_PER_SECTION and reduce the waste ;).
>
> Just to be clear, are you suggesting that we should use pfn_valid() on
> the pages within a section to calculate the actual range? The
> pfn_valid() implementation on arm64 checks for the validity of a sparse
> section, so this would be called from within the sparse_init() code
> path. I hope there's no dependency but I haven't checked. If it works,
> it's fine by me, it solves the FLATMEM mem_map freeing as well.
>
> With 4KB pages on arm64, vmemmap_populate() stops at the pmd level, so
> it always allocates PMD_SIZE. Wei's patch also only frees in PMD_SIZE
> amounts. So, with a sizeof(struct page) of 64 (2^6), a PMD_SIZE mem_map
> section would cover 2^(21-6) pages, so that's equivalent to a
> SECTION_SIZE_BITS of 21-6+12 = 27.
>
> If we reduce SECTION_SIZE_BITS to 27 or less, this patch is a no-op.
It would be the simplest way to fix this issue. It seems X86_64 is
also using 27.
@wei, has you ever tried to send a patch to change SECTION_SIZE_BITS
to 27 for ARM64?
>
> --
> Catalin
Thanks
Barry
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next prev parent reply other threads:[~2020-11-16 8:34 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-12 1:06 [PATCH v2] arm64: mm: free unused memmap for sparse memory model that define VMEMMAP Wei Li
2020-08-17 8:04 ` Mike Rapoport
2020-09-03 12:05 ` Catalin Marinas
2020-09-03 12:27 ` Mike Rapoport
2020-11-16 8:33 ` Song Bao Hua (Barry Song) [this message]
2020-11-16 8:42 ` 答复: " liwei (CM)
2020-11-16 10:46 ` Catalin Marinas
2020-11-23 3:45 ` 答复: " liwei (CM)
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