From: Hugh Dickins <hughd@google.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Hugh Dickins <hughd@google.com>,
Alistair Popple <apopple@nvidia.com>,
Jason Gunthorpe <jgg@nvidia.com>,
Ralph Campbell <rcampbell@nvidia.com>,
Christoph Hellwig <hch@lst.de>, Yang Shi <shy828301@gmail.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Shakeel Butt <shakeelb@google.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: [PATCH 2/4] mm/rmap: fix old bug: munlocking THP missed other mlocks
Date: Wed, 7 Jul 2021 13:08:53 -0700 (PDT) [thread overview]
Message-ID: <cfa154c-d595-406-eb7d-eb9df730f944@google.com> (raw)
In-Reply-To: <563ce5b2-7a44-5b4d-1dfd-59a0e65932a9@google.com>
The kernel recovers in due course from missing Mlocked pages: but there
was no point in calling page_mlock() (formerly known as try_to_munlock())
on a THP, because nothing got done even when it was found to be mapped in
another VM_LOCKED vma.
It's true that we need to be careful: Mlocked accounting of pte-mapped
THPs is too difficult (so consistently avoided); but Mlocked accounting
of only-pmd-mapped THPs is supposed to work, even when multiple mappings
are mlocked and munlocked or munmapped. Refine the tests.
There is already a VM_BUG_ON_PAGE(PageDoubleMap) in page_mlock(), so
page_mlock_one() does not even have to worry about that complication.
(I said the kernel recovers: but would page reclaim be likely to split
THP before rediscovering that it's VM_LOCKED? I've not followed that up.)
Fixes: 9a73f61bdb8a ("thp, mlock: do not mlock PTE-mapped file huge pages")
Signed-off-by: Hugh Dickins <hughd@google.com>
---
mm/rmap.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)
diff --git a/mm/rmap.c b/mm/rmap.c
index 746013e282c3..0e83c3be8568 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1442,8 +1442,9 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
*/
if (!(flags & TTU_IGNORE_MLOCK)) {
if (vma->vm_flags & VM_LOCKED) {
- /* PTE-mapped THP are never mlocked */
- if (!PageTransCompound(page)) {
+ /* PTE-mapped THP are never marked as mlocked */
+ if (!PageTransCompound(page) ||
+ (PageHead(page) && !PageDoubleMap(page))) {
/*
* Holding pte lock, we do *not* need
* mmap_lock here
@@ -1984,9 +1985,11 @@ static bool page_mlock_one(struct page *page, struct vm_area_struct *vma,
* munlock_vma_pages_range().
*/
if (vma->vm_flags & VM_LOCKED) {
- /* PTE-mapped THP are never mlocked */
- if (!PageTransCompound(page))
- mlock_vma_page(page);
+ /*
+ * PTE-mapped THP are never marked as mlocked, but
+ * this function is never called when PageDoubleMap().
+ */
+ mlock_vma_page(page);
page_vma_mapped_walk_done(&pvmw);
}
--
2.26.2
next prev parent reply other threads:[~2021-07-07 20:09 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-07 20:06 [PATCH 1/4] mm/rmap: fix comments left over from recent changes Hugh Dickins
2021-07-07 20:08 ` Hugh Dickins [this message]
2021-07-07 20:53 ` [PATCH 2/4] mm/rmap: fix old bug: munlocking THP missed other mlocks Shakeel Butt
2021-07-08 13:58 ` Kirill A. Shutemov
2021-07-09 2:50 ` Hugh Dickins
2021-07-09 10:56 ` Kirill A. Shutemov
2021-07-07 20:11 ` [PATCH 3/4] mm/rmap: fix new bug: premature return from page_mlock_one() Hugh Dickins
2021-07-07 20:22 ` Shakeel Butt
2021-07-07 23:14 ` Alistair Popple
2021-07-07 20:13 ` [PATCH 4/4] mm/rmap: try_to_migrate() skip zone_device !device_private Hugh Dickins
2021-07-07 20:54 ` Shakeel Butt
2021-07-07 23:25 ` Alistair Popple
2021-07-07 20:22 ` [PATCH 1/4] mm/rmap: fix comments left over from recent changes Shakeel Butt
2021-07-07 21:26 ` Yang Shi
2021-07-07 21:29 ` Yang Shi
2021-07-07 23:34 ` Alistair Popple
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