Messages in this thread | | | From | "Song Bao Hua (Barry Song)" <> | 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 |
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> -----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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