Hi, Barry I have changed SECTION_SIZE_BITS to 27 in our products, but I don't have to submit it.
-----邮件原件----- 发件人: Song Bao Hua (Barry Song) 发送时间: 2020年11月16日 16:34 收件人: Catalin Marinas <[email protected]>; Mike Rapoport <[email protected]>; liwei (CM) <[email protected]> 抄送: [email protected]; Xiaqing (A) <[email protected]>; Chenfeng (puck) <[email protected]>; butao <[email protected]>; fengbaopeng <[email protected]>; [email protected]; [email protected]; [email protected]; [email protected]; sujunfei <[email protected]>; Linuxarm <[email protected]> 主题: RE: [PATCH v2] arm64: mm: free unused memmap for sparse memory model that define VMEMMAP > -----Original Message----- > From: Catalin Marinas [mailto:[email protected]] > Sent: Friday, September 4, 2020 12:06 AM > To: Mike Rapoport <[email protected]> > Cc: liwei (CM) <[email protected]>; [email protected]; Xiaqing (A) > <[email protected]>; Chenfeng (puck) > <[email protected]>; butao <[email protected]>; fengbaopeng > <[email protected]>; [email protected]; > [email protected]; Song Bao Hua (Barry Song) > <[email protected]>; [email protected]; > [email protected]; sujunfei <[email protected]> > 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
