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From: Hugh Dickins <hughd@google.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	"Kirill A. Shutemov" <kirill@shutemov.name>,
	Matthew Wilcox <willy@infradead.org>,
	linux-mm@kvack.org
Subject: [PATCH 04/10] mm/khugepaged: collapse_shmem() stop if punched or truncated
Date: Mon, 26 Nov 2018 15:23:37 -0800 (PST)
Message-ID: <alpine.LSU.2.11.1811261522040.2275@eggly.anvils> (raw)
In-Reply-To: <alpine.LSU.2.11.1811261444420.2275@eggly.anvils>

Huge tmpfs testing showed that although collapse_shmem() recognizes a
concurrently truncated or hole-punched page correctly, its handling of
holes was liable to refill an emptied extent.  Add check to stop that.

Fixes: f3f0e1d2150b2 ("khugepaged: add support of collapse for tmpfs/shmem pages")
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: stable@vger.kernel.org # 4.8+
---
 mm/khugepaged.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index c13625c1ad5e..2070c316f06e 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1359,6 +1359,17 @@ static void collapse_shmem(struct mm_struct *mm,
 
 		VM_BUG_ON(index != xas.xa_index);
 		if (!page) {
+			/*
+			 * Stop if extent has been truncated or hole-punched,
+			 * and is now completely empty.
+			 */
+			if (index == start) {
+				if (!xas_next_entry(&xas, end - 1)) {
+					result = SCAN_TRUNCATED;
+					break;
+				}
+				xas_set(&xas, index);
+			}
 			if (!shmem_charge(mapping->host, 1)) {
 				result = SCAN_FAIL;
 				break;
-- 
2.20.0.rc0.387.gc7a69e6b6c-goog

  parent reply index

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-26 23:13 [PATCH 00/10] huge_memory,khugepaged tmpfs split/collapse fixes Hugh Dickins
2018-11-26 23:19 ` [PATCH 02/10] mm/huge_memory: splitting set mapping+index before unfreeze Hugh Dickins
2018-11-27  7:26   ` Kirill A. Shutemov
2018-11-26 23:21 ` [PATCH 03/10] mm/huge_memory: fix lockdep complaint on 32-bit i_size_read() Hugh Dickins
2018-11-27  7:27   ` Kirill A. Shutemov
2018-11-26 23:23 ` Hugh Dickins [this message]
2018-11-27  7:31   ` [PATCH 04/10] mm/khugepaged: collapse_shmem() stop if punched or truncated Kirill A. Shutemov
2018-11-27 13:26   ` Matthew Wilcox
2018-11-26 23:25 ` [PATCH 05/10] mm/khugepaged: fix crashes due to misaccounted holes Hugh Dickins
2018-11-27  7:35   ` Kirill A. Shutemov
2018-11-26 23:26 ` [PATCH 06/10] mm/khugepaged: collapse_shmem() remember to clear holes Hugh Dickins
2018-11-27  7:38   ` Kirill A. Shutemov
2018-11-26 23:27 ` [PATCH 07/10] mm/khugepaged: minor reorderings in collapse_shmem() Hugh Dickins
2018-11-27  7:59   ` Kirill A. Shutemov
2018-11-27 20:23     ` Hugh Dickins
2018-11-28 10:59       ` Kirill A. Shutemov
2018-11-28 19:40         ` Hugh Dickins
2018-11-26 23:29 ` [PATCH 08/10] mm/khugepaged: collapse_shmem() without freezing new_page Hugh Dickins
2018-11-27  8:01   ` Kirill A. Shutemov
2018-11-26 23:31 ` [PATCH 09/10] mm/khugepaged: collapse_shmem() do not crash on Compound Hugh Dickins
2018-11-26 23:33 ` [PATCH 10/10] mm/khugepaged: fix the xas_create_range() error path Hugh Dickins
2018-11-27  8:02   ` Kirill A. Shutemov

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