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Date: Mon, 7 Dec 2020 01:40:35 +0000 From: "Song Bao Hua (Barry Song)" <song.bao.hua@...ilicon.com> To: Mike Rapoport <rppt@...ux.ibm.com>, Will Deacon <will@...nel.org> CC: "liwei (CM)" <liwei213@...wei.com>, "catalin.marinas@....com" <catalin.marinas@....com>, fengbaopeng <fengbaopeng2@...ilicon.com>, "nsaenzjulienne@...e.de" <nsaenzjulienne@...e.de>, "steve.capper@....com" <steve.capper@....com>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, butao <butao@...ilicon.com> Subject: RE: [PATCH] arm64: mm: decrease the section size to reduce the memory reserved for the page map > -----Original Message----- > From: Mike Rapoport [mailto:rppt@...ux.ibm.com] > Sent: Saturday, December 5, 2020 12:44 AM > To: Will Deacon <will@...nel.org> > Cc: liwei (CM) <liwei213@...wei.com>; catalin.marinas@....com; fengbaopeng > <fengbaopeng2@...ilicon.com>; nsaenzjulienne@...e.de; steve.capper@....com; > Song Bao Hua (Barry Song) <song.bao.hua@...ilicon.com>; > linux-arm-kernel@...ts.infradead.org; linux-kernel@...r.kernel.org; butao > <butao@...ilicon.com> > Subject: Re: [PATCH] arm64: mm: decrease the section size to reduce the memory > reserved for the page map > > On Fri, Dec 04, 2020 at 11:13:47AM +0000, Will Deacon 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@...wei.com> > > > Signed-off-by: Baopeng Feng <fengbaopeng2@...ilicon.com> > > > Signed-off-by: Xia Qing <saberlily.xia@...ilicon.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? > > I think that for 64-bit there are still plenty of free bits. I didn't > check now, but when I played with SPARSEMEM on m68k there were 8 bits > for section out of 32. > > > 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. > > I don't think it's related to NR_CPUS and NODES_SHIFT. > This seems rather 64K pages that cause this. > > Not that is shouldn't be addressed. Right now, only 4K PAGES will define ARM64_SWAPPER_USES_SECTION_MAPS. Other cases will use vmemmap_populate_basepages(). The original patch should be only addressing the issue in 4K pages: https://lore.kernel.org/lkml/20200812010655.96339-1-liwei213@huawei.com/ would we do something like the below? #ifdef CONFIG_ARM64_4K_PAGE #define SECTION_SIZE_BITS 27 #else #define SECTION_SIZE_BITS 30 #endif > > > Will > > -- > Sincerely yours, > Mike. Thanks Barry
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