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SubjectRe: [PATCH v2 1/5] mm: page_alloc: remain memblock_next_valid_pfn() when CONFIG_HAVE_ARCH_PFN_VALID is enable
On Sat, Mar 24, 2018 at 05:24:38AM -0700, Jia He wrote:
>Commit b92df1de5d28 ("mm: page_alloc: skip over regions of invalid pfns
>where possible") optimized the loop in memmap_init_zone(). But it causes
>possible panic bug. So Daniel Vacek reverted it later.
>

Why this has a bug? Do you have some link about it?

If the audience could know the potential risk, it would be helpful to review
the code and decide whether to take it back.

>But memblock_next_valid_pfn is valid when CONFIG_HAVE_ARCH_PFN_VALID is
>enabled. And as verified by Eugeniu Rosca, arm can benifit from this
>commit. So remain the memblock_next_valid_pfn.
>
>Signed-off-by: Jia He <jia.he@hxt-semitech.com>
>---
> include/linux/memblock.h | 4 ++++
> mm/memblock.c | 29 +++++++++++++++++++++++++++++
> mm/page_alloc.c | 11 ++++++++++-
> 3 files changed, 43 insertions(+), 1 deletion(-)
>
>diff --git a/include/linux/memblock.h b/include/linux/memblock.h
>index 0257aee..efbbe4b 100644
>--- a/include/linux/memblock.h
>+++ b/include/linux/memblock.h
>@@ -203,6 +203,10 @@ void __next_mem_pfn_range(int *idx, int nid, unsigned long *out_start_pfn,
> i >= 0; __next_mem_pfn_range(&i, nid, p_start, p_end, p_nid))
> #endif /* CONFIG_HAVE_MEMBLOCK_NODE_MAP */
>
>+#ifdef CONFIG_HAVE_ARCH_PFN_VALID
>+unsigned long memblock_next_valid_pfn(unsigned long pfn);
>+#endif
>+
> /**
> * for_each_free_mem_range - iterate through free memblock areas
> * @i: u64 used as loop variable
>diff --git a/mm/memblock.c b/mm/memblock.c
>index ba7c878..bea5a9c 100644
>--- a/mm/memblock.c
>+++ b/mm/memblock.c
>@@ -1102,6 +1102,35 @@ void __init_memblock __next_mem_pfn_range(int *idx, int nid,
> *out_nid = r->nid;
> }
>
>+#ifdef CONFIG_HAVE_ARCH_PFN_VALID
>+unsigned long __init_memblock memblock_next_valid_pfn(unsigned long pfn)
>+{
>+ struct memblock_type *type = &memblock.memory;
>+ unsigned int right = type->cnt;
>+ unsigned int mid, left = 0;
>+ phys_addr_t addr = PFN_PHYS(++pfn);
>+
>+ do {
>+ mid = (right + left) / 2;
>+
>+ if (addr < type->regions[mid].base)
>+ right = mid;
>+ else if (addr >= (type->regions[mid].base +
>+ type->regions[mid].size))
>+ left = mid + 1;
>+ else {
>+ /* addr is within the region, so pfn is valid */
>+ return pfn;
>+ }
>+ } while (left < right);
>+
>+ if (right == type->cnt)
>+ return -1UL;
>+ else
>+ return PHYS_PFN(type->regions[right].base);
>+}
>+#endif /*CONFIG_HAVE_ARCH_PFN_VALID*/
>+
> /**
> * memblock_set_node - set node ID on memblock regions
> * @base: base of area to set node ID for
>diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>index c19f5ac..2a967f7 100644
>--- a/mm/page_alloc.c
>+++ b/mm/page_alloc.c
>@@ -5483,8 +5483,17 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
> if (context != MEMMAP_EARLY)
> goto not_early;
>
>- if (!early_pfn_valid(pfn))
>+ if (!early_pfn_valid(pfn)) {
>+#if (defined CONFIG_HAVE_MEMBLOCK) && (defined CONFIG_HAVE_ARCH_PFN_VALID)

In commit b92df1de5d28, it use CONFIG_HAVE_MEMBLOCK_NODE_MAP.

Not get the point of your change.


>+ /*
>+ * Skip to the pfn preceding the next valid one (or
>+ * end_pfn), such that we hit a valid pfn (or end_pfn)
>+ * on our next iteration of the loop.
>+ */
>+ pfn = memblock_next_valid_pfn(pfn) - 1;
>+#endif
> continue;
>+ }
> if (!early_pfn_in_nid(pfn, nid))
> continue;
> if (!update_defer_init(pgdat, pfn, end_pfn, &nr_initialised))
>--
>2.7.4

--
Wei Yang
Help you, Help me

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