linux-kernel - [PATCH v6 14/14] selftests/vm: test faulting in kernel, and verify pinnable pages

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Message-Id: <20210120014333.222547-15-pasha.tatashin@soleen.com>
Date:   Tue, 19 Jan 2021 20:43:33 -0500
From:   Pavel Tatashin <pasha.tatashin@...een.com>
To:     pasha.tatashin@...een.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, akpm@...ux-foundation.org, vbabka@...e.cz,
        mhocko@...e.com, david@...hat.com, osalvador@...e.de,
        dan.j.williams@...el.com, sashal@...nel.org,
        tyhicks@...ux.microsoft.com, iamjoonsoo.kim@....com,
        mike.kravetz@...cle.com, rostedt@...dmis.org, mingo@...hat.com,
        jgg@...pe.ca, peterz@...radead.org, mgorman@...e.de,
        willy@...radead.org, rientjes@...gle.com, jhubbard@...dia.com,
        linux-doc@...r.kernel.org, ira.weiny@...el.com,
        linux-kselftest@...r.kernel.org
Subject: [PATCH v6 14/14] selftests/vm: test faulting in kernel, and verify pinnable pages

When pages are pinned they can be faulted in userland and migrated, and
they can be faulted right in kernel without migration.

In either case, the pinned pages must end-up being pinnable (not movable).

Add a new test to gup_test, to help verify that the gup/pup
(get_user_pages() / pin_user_pages()) behavior with respect to pinnable
and movable pages is reasonable and correct. Specifically, provide a
way to:

1) Verify that only "pinnable" pages are pinned. This is checked
automatically for you.

2) Verify that gup/pup performance is reasonable. This requires
comparing benchmarks between doing gup/pup on pages that have been
pre-faulted in from user space, vs. doing gup/pup on pages that are not
faulted in until gup/pup time (via FOLL_TOUCH). This decision is
controlled with the new -z command line option.

Signed-off-by: Pavel Tatashin <pasha.tatashin@...een.com>
---
 mm/gup_test.c                         |  6 ++++++
 tools/testing/selftests/vm/gup_test.c | 23 +++++++++++++++++++----
 2 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/mm/gup_test.c b/mm/gup_test.c
index a6ed1c877679..d974dec19e1c 100644
--- a/mm/gup_test.c
+++ b/mm/gup_test.c
@@ -52,6 +52,12 @@ static void verify_dma_pinned(unsigned int cmd, struct page **pages,
 
 				dump_page(page, "gup_test failure");
 				break;
+			} else if (cmd == PIN_LONGTERM_BENCHMARK &&
+				WARN(!is_pinnable_page(page),
+				     "pages[%lu] is NOT pinnable but pinned\n",
+				     i)) {
+				dump_page(page, "gup_test failure");
+				break;
 			}
 		}
 		break;
diff --git a/tools/testing/selftests/vm/gup_test.c b/tools/testing/selftests/vm/gup_test.c
index 943cc2608dc2..1e662d59c502 100644
--- a/tools/testing/selftests/vm/gup_test.c
+++ b/tools/testing/selftests/vm/gup_test.c
@@ -13,6 +13,7 @@
 
 /* Just the flags we need, copied from mm.h: */
 #define FOLL_WRITE	0x01	/* check pte is writable */
+#define FOLL_TOUCH	0x02	/* mark page accessed */
 
 static char *cmd_to_str(unsigned long cmd)
 {
@@ -39,11 +40,11 @@ int main(int argc, char **argv)
 	unsigned long size = 128 * MB;
 	int i, fd, filed, opt, nr_pages = 1, thp = -1, repeats = 1, write = 1;
 	unsigned long cmd = GUP_FAST_BENCHMARK;
-	int flags = MAP_PRIVATE;
+	int flags = MAP_PRIVATE, touch = 0;
 	char *file = "/dev/zero";
 	char *p;
 
-	while ((opt = getopt(argc, argv, "m:r:n:F:f:abctTLUuwWSHp")) != -1) {
+	while ((opt = getopt(argc, argv, "m:r:n:F:f:abctTLUuwWSHpz")) != -1) {
 		switch (opt) {
 		case 'a':
 			cmd = PIN_FAST_BENCHMARK;
@@ -110,6 +111,10 @@ int main(int argc, char **argv)
 		case 'H':
 			flags |= (MAP_HUGETLB | MAP_ANONYMOUS);
 			break;
+		case 'z':
+			/* fault pages in gup, do not fault in userland */
+			touch = 1;
+			break;
 		default:
 			return -1;
 		}
@@ -167,8 +172,18 @@ int main(int argc, char **argv)
 	else if (thp == 0)
 		madvise(p, size, MADV_NOHUGEPAGE);
 
-	for (; (unsigned long)p < gup.addr + size; p += PAGE_SIZE)
-		p[0] = 0;
+	/*
+	 * FOLL_TOUCH, in gup_test, is used as an either/or case: either
+	 * fault pages in from the kernel via FOLL_TOUCH, or fault them
+	 * in here, from user space. This allows comparison of performance
+	 * between those two cases.
+	 */
+	if (touch) {
+		gup.gup_flags |= FOLL_TOUCH;
+	} else {
+		for (; (unsigned long)p < gup.addr + size; p += PAGE_SIZE)
+			p[0] = 0;
+	}
 
 	/* Only report timing information on the *_BENCHMARK commands: */
 	if ((cmd == PIN_FAST_BENCHMARK) || (cmd == GUP_FAST_BENCHMARK) ||
-- 
2.25.1