linux-kernel - [PATCH v2] mm: replace is_zero_pfn with is_huge_zero

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Message-Id: <20191108192629.201556-1-yuzhao@google.com>
Date:   Fri,  8 Nov 2019 12:26:29 -0700
From:   Yu Zhao <yuzhao@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Ralph Campbell <rcampbell@...dia.com>,
        "Jérôme Glisse" <jglisse@...hat.com>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        Dave Airlie <airlied@...hat.com>,
        Thomas Hellstrom <thellstrom@...are.com>,
        Souptick Joarder <jrdr.linux@...il.com>,
        Gerald Schaefer <gerald.schaefer@...ibm.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Yu Zhao <yuzhao@...gle.com>
Subject: [PATCH v2] mm: 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.

Signed-off-by: Yu Zhao <yuzhao@...gle.com>
---
 mm/memory.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/memory.c b/mm/memory.c
index b1ca51a079f2..cf209f84ce4a 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -654,7 +654,7 @@ struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr,
 
 	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;
-- 
2.24.0.rc1.363.gb1bccd3e3d-goog