sparsemem hotplug base
Subsystems (3)
PATCH 6/6 sparsemem hotplug base
Make sparse's initalization be accessible at runtime. This allows sparse mappings to be created after boot in a hotplug situation.
This patch is separated from the previous one just to give an indication how much of the sparse infrastructure is *just* for hotplug memory.
The section_mem_map doesn't really store a pointer. It stores something that is convenient to do some math against to get a pointer. It isn't valid to just do *section_mem_map, so I don't think it should be stored as a pointer.
There are a couple of things I'd like to store about a section. First of all, the fact that it is !NULL does not mean that it is present. There could be such a combination where section_mem_map *is* NULL, but the math gets you properly to a real mem_map. So, I don't think that check is safe.
Since we're storing 32-bit-aligned structures, we have a few bits in the bottom of the pointer to play with. Use one bit to encode whether there's really a mem_map there, and the other one to tell whether there's a valid section there. We need to distinguish between the two because sometimes there's a gap between when a section is discovered to be present and when we can get the mem_map for it.
--- include/linux/mmzone.h | 48 +++++++++++++++++++++++-- mm/sparse.c | 92 ++++++++++++++++++++++++++++++++++++++----------- 2 files changed, 116 insertions(+), 24 deletions(-)
include/linux/mmzone.h +44 -4
@@ -459,12 +459,52 @@ extern struct pglist_data contig_page_dastruct page ;struct mem_section { -struct page *section_mem_map; +/* +* This is, logically, a pointer to an array of struct +* pages. However, it is stored with some other magic. +* (see sparse.c::sparse_init_one_section()) +* +* Making it a UL at least makes someone do a cast +* before using it wrong. +*/ +unsigned long section_mem_map; };extern struct mem_section mem_section[NR_MEM_SECTIONS ];/* +* We use the lower bits of the mem_map pointer to store +* a little bit of information. There should be at least +* 3 bits here due to 32-bit alignment. +*/ +#define SECTION_MARKED_PRESENT (1UL<<0) +#define SECTION_HAS_MEM_MAP (1UL<<1) +#define SECTION_MAP_LAST_BIT (1UL<<2) +#define SECTION_MAP_MASK (~(SECTION_MAP_LAST_BIT-1)) + +static inline struct page *__section_mem_map_addr (struct mem_section *section) +{ +unsigned long map = section->section_mem_map; + map &=SECTION_MAP_MASK ; +return (struct page *)map; +} + +static inline int valid_section (struct mem_section *section) +{ +return (section->section_mem_map &SECTION_MARKED_PRESENT ); +} + +static inline int section_has_mem_map (struct mem_section *section) +{ +return (section->section_mem_map &SECTION_HAS_MEM_MAP ); +} + +static inline int valid_section_nr (int nr) +{ +return valid_section (&mem_section[nr]); +} + +/* * Given a kernel address, find the home node of the underlying memory. */ #define kvaddr_to_nid (kaddr) pfn_to_nid(__pa(kaddr) >> PAGE_SHIFT)
@@ -477,18 +517,18 @@ static inline struct mem_section *__pfn_#define pfn_to_page (pfn) \ ({ \ unsigned long __pfn = (pfn); \ - __pfn_to_section(__pfn)->section_mem_map + __pfn; \ + __section_mem_map_addr(__pfn_to_section(__pfn)) + __pfn; \ })#define page_to_pfn (page) \ ({ \ - page - mem_section[page_to_section(page)].section_mem_map; \ + page - __section_mem_map_addr(&mem_section[page_to_section(page)]); \ })static inline int pfn_valid (unsigned long pfn) {if (pfn_to_section_nr (pfn) >=NR_MEM_SECTIONS )return 0 ; -return mem_section[pfn_to_section_nr (pfn)].section_mem_map !=0 ; +return valid_section (&mem_section[pfn_to_section_nr (pfn)]); }/*
mm/sparse.c +72 -20
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