On Tue 10-10-17 15:44:41, Michal Hocko wrote: > On Mon 09-10-17 18:19:27, Pavel Tatashin wrote: > > Some memory is reserved but unavailable: not present in memblock.memory > > (because not backed by physical pages), but present in memblock.reserved. > > Such memory has backing struct pages, but they are not initialized by going > > through __init_single_page(). > > > > In some cases these struct pages are accessed even if they do not contain > > any data. One example is page_to_pfn() might access page->flags if this is > > where section information is stored (CONFIG_SPARSEMEM, > > SECTION_IN_PAGE_FLAGS). > > > > One example of such memory: trim_low_memory_range() unconditionally > > reserves from pfn 0, but e820__memblock_setup() might provide the exiting > > memory from pfn 1 (i.e. KVM). Btw. I would add your example from http://lkml.kernel.org/r/bcf24369-ac37-cedd-a264-3396fb5cf39e@xxxxxxxxxx to do changelog > > Since, struct pages are zeroed in __init_single_page(), and not during > > allocation time, we must zero such struct pages explicitly. > > > > The patch involves adding a new memblock iterator: > > for_each_resv_unavail_range(i, p_start, p_end) > > > > Which iterates through reserved && !memory lists, and we zero struct pages > > explicitly by calling mm_zero_struct_page(). > > > > Signed-off-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx> > > Reviewed-by: Steven Sistare <steven.sistare@xxxxxxxxxx> > > Reviewed-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx> > > Reviewed-by: Bob Picco <bob.picco@xxxxxxxxxx> > > Acked-by: Michal Hocko <mhocko@xxxxxxxx> > > > --- > > include/linux/memblock.h | 16 ++++++++++++++++ > > include/linux/mm.h | 15 +++++++++++++++ > > mm/page_alloc.c | 38 ++++++++++++++++++++++++++++++++++++++ > > 3 files changed, 69 insertions(+) > > > > diff --git a/include/linux/memblock.h b/include/linux/memblock.h > > index bae11c7e7bf3..ce8bfa5f3e9b 100644 > > --- a/include/linux/memblock.h > > +++ b/include/linux/memblock.h > > @@ -237,6 +237,22 @@ unsigned long memblock_next_valid_pfn(unsigned long pfn, unsigned long max_pfn); > > for_each_mem_range_rev(i, &memblock.memory, &memblock.reserved, \ > > nid, flags, p_start, p_end, p_nid) > > > > +/** > > + * for_each_resv_unavail_range - iterate through reserved and unavailable memory > > + * @i: u64 used as loop variable > > + * @flags: pick from blocks based on memory attributes > > + * @p_start: ptr to phys_addr_t for start address of the range, can be %NULL > > + * @p_end: ptr to phys_addr_t for end address of the range, can be %NULL > > + * > > + * Walks over unavailable but reserved (reserved && !memory) areas of memblock. > > + * Available as soon as memblock is initialized. > > + * Note: because this memory does not belong to any physical node, flags and > > + * nid arguments do not make sense and thus not exported as arguments. > > + */ > > +#define for_each_resv_unavail_range(i, p_start, p_end) \ > > + for_each_mem_range(i, &memblock.reserved, &memblock.memory, \ > > + NUMA_NO_NODE, MEMBLOCK_NONE, p_start, p_end, NULL) > > + > > static inline void memblock_set_region_flags(struct memblock_region *r, > > unsigned long flags) > > { > > diff --git a/include/linux/mm.h b/include/linux/mm.h > > index 065d99deb847..04c8b2e5aff4 100644 > > --- a/include/linux/mm.h > > +++ b/include/linux/mm.h > > @@ -94,6 +94,15 @@ extern int mmap_rnd_compat_bits __read_mostly; > > #define mm_forbids_zeropage(X) (0) > > #endif > > > > +/* > > + * On some architectures it is expensive to call memset() for small sizes. > > + * Those architectures should provide their own implementation of "struct page" > > + * zeroing by defining this macro in <asm/pgtable.h>. > > + */ > > +#ifndef mm_zero_struct_page > > +#define mm_zero_struct_page(pp) ((void)memset((pp), 0, sizeof(struct page))) > > +#endif > > + > > /* > > * Default maximum number of active map areas, this limits the number of vmas > > * per mm struct. Users can overwrite this number by sysctl but there is a > > @@ -2001,6 +2010,12 @@ extern int __meminit __early_pfn_to_nid(unsigned long pfn, > > struct mminit_pfnnid_cache *state); > > #endif > > > > +#ifdef CONFIG_HAVE_MEMBLOCK > > +void zero_resv_unavail(void); > > +#else > > +static inline void zero_resv_unavail(void) {} > > +#endif > > + > > extern void set_dma_reserve(unsigned long new_dma_reserve); > > extern void memmap_init_zone(unsigned long, int, unsigned long, > > unsigned long, enum memmap_context); > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > index 20b0bace2235..5f0013bbbe9d 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -6209,6 +6209,42 @@ void __paginginit free_area_init_node(int nid, unsigned long *zones_size, > > free_area_init_core(pgdat); > > } > > > > +#ifdef CONFIG_HAVE_MEMBLOCK > > +/* > > + * Only struct pages that are backed by physical memory are zeroed and > > + * initialized by going through __init_single_page(). But, there are some > > + * struct pages which are reserved in memblock allocator and their fields > > + * may be accessed (for example page_to_pfn() on some configuration accesses > > + * flags). We must explicitly zero those struct pages. > > + */ > > +void __paginginit zero_resv_unavail(void) > > +{ > > + phys_addr_t start, end; > > + unsigned long pfn; > > + u64 i, pgcnt; > > + > > + /* Loop through ranges that are reserved, but do not have reported > > + * physical memory backing. > > + */ > > + pgcnt = 0; > > + for_each_resv_unavail_range(i, &start, &end) { > > + for (pfn = PFN_DOWN(start); pfn < PFN_UP(end); pfn++) { > > + mm_zero_struct_page(pfn_to_page(pfn)); > > + pgcnt++; > > + } > > + } > > + > > + /* > > + * Struct pages that do not have backing memory. This could be because > > + * firmware is using some of this memory, or for some other reasons. > > + * Once memblock is changed so such behaviour is not allowed: i.e. > > + * list of "reserved" memory must be a subset of list of "memory", then > > + * this code can be removed. > > + */ > > + pr_info("Reserved but unavailable: %lld pages", pgcnt); > > +} > > +#endif /* CONFIG_HAVE_MEMBLOCK */ > > + > > #ifdef CONFIG_HAVE_MEMBLOCK_NODE_MAP > > > > #if MAX_NUMNODES > 1 > > @@ -6632,6 +6668,7 @@ void __init free_area_init_nodes(unsigned long *max_zone_pfn) > > node_set_state(nid, N_MEMORY); > > check_for_memory(pgdat, nid); > > } > > + zero_resv_unavail(); > > } > > > > static int __init cmdline_parse_core(char *p, unsigned long *core) > > @@ -6795,6 +6832,7 @@ void __init free_area_init(unsigned long *zones_size) > > { > > free_area_init_node(0, zones_size, > > __pa(PAGE_OFFSET) >> PAGE_SHIFT, NULL); > > + zero_resv_unavail(); > > } > > > > static int page_alloc_cpu_dead(unsigned int cpu) > > -- > > 2.14.2 > > -- > Michal Hocko > SUSE Labs -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
