Re: [PATCH v2 1/5] mm: page_alloc: remain memblock_next_valid_pfn() when CONFIG_HAVE_ARCH_PFN_VALID is enable

[Wei Yang]

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@xxxxxxxxxxxxxxxx>
>---
> 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