From: Anshuman Khandual <anshuman.khandual@arm.com>
To: linux-mm@kvack.org, linux-kernel@vger.kernel.org
Cc: kirill.shutemov@linux.intel.com, akpm@linux-foundation.org,
mhocko@suse.com, zi.yan@cs.rutgers.edu, will.deacon@arm.com
Subject: [PATCH] mm/thp: Correctly differentiate between mapped THP and PMD migration entry
Date: Tue, 9 Oct 2018 09:28:58 +0530 [thread overview]
Message-ID: <1539057538-27446-1-git-send-email-anshuman.khandual@arm.com> (raw)
A normal mapped THP page at PMD level should be correctly differentiated
from a PMD migration entry while walking the page table. A mapped THP would
additionally check positive for pmd_present() along with pmd_trans_huge()
as compared to a PMD migration entry. This just adds a new conditional test
differentiating the two while walking the page table.
Fixes: 616b8371539a6 ("mm: thp: enable thp migration in generic path")
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
---
On X86, pmd_trans_huge() and is_pmd_migration_entry() are always mutually
exclusive which makes the current conditional block work for both mapped
and migration entries. This is not same with arm64 where pmd_trans_huge()
returns positive for both mapped and migration entries. Could some one
please explain why pmd_trans_huge() has to return false for migration
entries which just install swap bits and its still a PMD ? Nonetheless
pmd_present() seems to be a better check to distinguish between mapped
and (non-mapped non-present) migration entries without any ambiguity.
mm/page_vma_mapped.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
index ae3c2a3..b384396 100644
--- a/mm/page_vma_mapped.c
+++ b/mm/page_vma_mapped.c
@@ -161,7 +161,8 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
pmde = READ_ONCE(*pvmw->pmd);
if (pmd_trans_huge(pmde) || is_pmd_migration_entry(pmde)) {
pvmw->ptl = pmd_lock(mm, pvmw->pmd);
- if (likely(pmd_trans_huge(*pvmw->pmd))) {
+ if (likely(pmd_trans_huge(*pvmw->pmd) &&
+ pmd_present(*pvmw->pmd))) {
if (pvmw->flags & PVMW_MIGRATION)
return not_found(pvmw);
if (pmd_page(*pvmw->pmd) != page)
--
2.7.4
next reply other threads:[~2018-10-09 3:59 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-09 3:58 Anshuman Khandual [this message]
2018-10-09 13:04 ` [PATCH] mm/thp: Correctly differentiate between mapped THP and PMD migration entry Kirill A. Shutemov
2018-10-09 13:18 ` Will Deacon
2018-10-12 8:02 ` Anshuman Khandual
2018-10-15 8:32 ` Aneesh Kumar K.V
2018-10-16 13:16 ` Anshuman Khandual
2018-10-09 13:42 ` Anshuman Khandual
2018-10-09 13:58 ` Zi Yan
2018-10-10 4:05 ` Anshuman Khandual
2018-10-10 12:43 ` Zi Yan
2018-10-12 8:00 ` Anshuman Khandual
2018-10-15 0:53 ` Zi Yan
2018-10-15 4:06 ` Anshuman Khandual
2018-10-16 14:31 ` Zi Yan
2018-10-18 2:17 ` Naoya Horiguchi
2018-11-02 5:22 ` Anshuman Khandual
2018-10-25 8:10 ` Anshuman Khandual
2018-10-25 18:45 ` Zi Yan
2018-10-26 1:39 ` Anshuman Khandual
2018-10-17 2:09 ` Andrea Arcangeli
2018-10-22 14:00 ` Zi Yan
2018-11-02 6:15 ` Anshuman Khandual
2018-11-06 0:35 ` Will Deacon
2018-11-06 9:51 ` Anshuman Khandual
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