[patch 05/86] mm/memory.c: replace is_zero_pfn with is_huge_zero_pmd for thp

Andrew Morton
2019-12-05T00:49:59Z

From: Yu Zhao <yuzhao@google.com>
Subject: mm/memory.c: replace is_zero_pfn with is_huge_zero_pmd for thp

For hugely mapped thp, we use is_huge_zero_pmd() to check if it's zero
page or not.

We do fill ptes with my_zero_pfn() when we split zero thp pmd, but this is
not what we have in vm_normal_page_pmd() -- pmd_trans_huge_lock() makes
sure of it.

This is a trivial fix for /proc/pid/numa_maps, and AFAIK nobody complains
about it.

Gerald Schaefer asked:
: Maybe the description could also mention the symptom of this bug?
: I would assume that it affects anon/dirty accounting in gather_pte_stats(),
: for huge mappings, if zero page mappings are not correctly recognized.

I came across this while I was looking at the code, so I'm not aware of
any symptom.

Link: http://lkml.kernel.org/r/20191108192629.201556-1-yuzhao@google.com
Signed-off-by: Yu Zhao <yuzhao@google.com>
Acked-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Will Deacon <will@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: "Aneesh Kumar K . V" <aneesh.kumar@linux.ibm.com>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Thomas Hellstrom <thellstrom@vmware.com>
Cc: Souptick Joarder <jrdr.linux@gmail.com>
Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

mm/memory.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/memory.c~mm-replace-is_zero_pfn-with-is_huge_zero_pmd-for-thp
+++ a/mm/memory.c
@@ -672,7 +672,7 @@ struct page *vm_normal_page_pmd(struct v

if (pmd_devmap(pmd))
return NULL;
- if (is_zero_pfn(pfn))
+ if (is_huge_zero_pmd(pmd))
return NULL;
if (unlikely(pfn > highest_memmap_pfn))
return NULL;
_