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Date: Tue, 10 Oct 2017 16:09:42 +0200
From: Michal Hocko <mhocko@...nel.org>
To: Pavel Tatashin <pasha.tatashin@...cle.com>
Cc: linux-kernel@...r.kernel.org, sparclinux@...r.kernel.org,
linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org,
linux-s390@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
x86@...nel.org, kasan-dev@...glegroups.com, borntraeger@...ibm.com,
heiko.carstens@...ibm.com, davem@...emloft.net,
willy@...radead.org, ard.biesheuvel@...aro.org,
mark.rutland@....com, will.deacon@....com, catalin.marinas@....com,
sam@...nborg.org, mgorman@...hsingularity.net,
steven.sistare@...cle.com, daniel.m.jordan@...cle.com,
bob.picco@...cle.com
Subject: Re: [PATCH v11 5/9] mm: zero reserved and unavailable struct pages
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@oracle.com
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@...cle.com>
> > Reviewed-by: Steven Sistare <steven.sistare@...cle.com>
> > Reviewed-by: Daniel Jordan <daniel.m.jordan@...cle.com>
> > Reviewed-by: Bob Picco <bob.picco@...cle.com>
>
> Acked-by: Michal Hocko <mhocko@...e.com>
>
> > ---
> > 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
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