linux-kernel - [PATCH v2 4/4] tools/testing/selftests: add VMA merge tests for KSM merge

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Message-ID: <cbe5274aa4440be230d87a2b48aaef2b6d73403e.1747844463.git.lorenzo.stoakes@oracle.com>
Date: Wed, 21 May 2025 19:20:31 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
        Pedro Falcato <pfalcato@...e.de>, David Hildenbrand <david@...hat.com>,
        Xu Xin <xu.xin16@....com.cn>,
        Chengming Zhou <chengming.zhou@...ux.dev>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Stefan Roesch <shr@...kernel.io>
Subject: [PATCH v2 4/4] tools/testing/selftests: add VMA merge tests for KSM merge

Add test to assert that we have now allowed merging of VMAs when KSM
merging-by-default has been set by prctl(PR_SET_MEMORY_MERGE, ...).

We simply perform a trivial mapping of adjacent VMAs expecting a merge,
however prior to recent changes implementing this mode earlier than before,
these merges would not have succeeded.

Assert that we have fixed this!

Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Reviewed-by: Chengming Zhou <chengming.zhou@...ux.dev>
Tested-by: Chengming Zhou <chengming.zhou@...ux.dev>
---
 tools/testing/selftests/mm/merge.c | 78 ++++++++++++++++++++++++++++++
 1 file changed, 78 insertions(+)

diff --git a/tools/testing/selftests/mm/merge.c b/tools/testing/selftests/mm/merge.c
index c76646cdf6e6..2380a5a6a529 100644
--- a/tools/testing/selftests/mm/merge.c
+++ b/tools/testing/selftests/mm/merge.c
@@ -2,10 +2,12 @@
 
 #define _GNU_SOURCE
 #include "../kselftest_harness.h"
+#include <linux/prctl.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
 #include <sys/mman.h>
+#include <sys/prctl.h>
 #include <sys/wait.h>
 #include "vm_util.h"
 
@@ -31,6 +33,11 @@ FIXTURE_TEARDOWN(merge)
 {
 	ASSERT_EQ(munmap(self->carveout, 12 * self->page_size), 0);
 	ASSERT_EQ(close_procmap(&self->procmap), 0);
+	/*
+	 * Clear unconditionally, as some tests set this. It is no issue if this
+	 * fails (KSM may be disabled for instance).
+	 */
+	prctl(PR_SET_MEMORY_MERGE, 0, 0, 0, 0);
 }
 
 TEST_F(merge, mprotect_unfaulted_left)
@@ -452,4 +459,75 @@ TEST_F(merge, forked_source_vma)
 	ASSERT_EQ(procmap->query.vma_end, (unsigned long)ptr2 + 5 * page_size);
 }
 
+TEST_F(merge, ksm_merge)
+{
+	unsigned int page_size = self->page_size;
+	char *carveout = self->carveout;
+	struct procmap_fd *procmap = &self->procmap;
+	char *ptr, *ptr2;
+	int err;
+
+	/*
+	 * Map two R/W immediately adjacent to one another, they should
+	 * trivially merge:
+	 *
+	 * |-----------|-----------|
+	 * |    R/W    |    R/W    |
+	 * |-----------|-----------|
+	 *      ptr         ptr2
+	 */
+
+	ptr = mmap(&carveout[page_size], page_size, PROT_READ | PROT_WRITE,
+		   MAP_ANON | MAP_PRIVATE | MAP_FIXED, -1, 0);
+	ASSERT_NE(ptr, MAP_FAILED);
+	ptr2 = mmap(&carveout[2 * page_size], page_size,
+		    PROT_READ | PROT_WRITE,
+		    MAP_ANON | MAP_PRIVATE | MAP_FIXED, -1, 0);
+	ASSERT_NE(ptr2, MAP_FAILED);
+	ASSERT_TRUE(find_vma_procmap(procmap, ptr));
+	ASSERT_EQ(procmap->query.vma_start, (unsigned long)ptr);
+	ASSERT_EQ(procmap->query.vma_end, (unsigned long)ptr + 2 * page_size);
+
+	/* Unmap the second half of this merged VMA. */
+	ASSERT_EQ(munmap(ptr2, page_size), 0);
+
+	/* OK, now enable global KSM merge. We clear this on test teardown. */
+	err = prctl(PR_SET_MEMORY_MERGE, 1, 0, 0, 0);
+	if (err == -1) {
+		int errnum = errno;
+
+		/* Only non-failure case... */
+		ASSERT_EQ(errnum, EINVAL);
+		/* ...but indicates we should skip. */
+		SKIP(return, "KSM memory merging not supported, skipping.");
+	}
+
+	/*
+	 * Now map a VMA adjacent to the existing that was just made
+	 * VM_MERGEABLE, this should merge as well.
+	 */
+	ptr2 = mmap(&carveout[2 * page_size], page_size,
+		    PROT_READ | PROT_WRITE,
+		    MAP_ANON | MAP_PRIVATE | MAP_FIXED, -1, 0);
+	ASSERT_NE(ptr2, MAP_FAILED);
+	ASSERT_TRUE(find_vma_procmap(procmap, ptr));
+	ASSERT_EQ(procmap->query.vma_start, (unsigned long)ptr);
+	ASSERT_EQ(procmap->query.vma_end, (unsigned long)ptr + 2 * page_size);
+
+	/* Now this VMA altogether. */
+	ASSERT_EQ(munmap(ptr, 2 * page_size), 0);
+
+	/* Try the same operation as before, asserting this also merges fine. */
+	ptr = mmap(&carveout[page_size], page_size, PROT_READ | PROT_WRITE,
+		   MAP_ANON | MAP_PRIVATE | MAP_FIXED, -1, 0);
+	ASSERT_NE(ptr, MAP_FAILED);
+	ptr2 = mmap(&carveout[2 * page_size], page_size,
+		    PROT_READ | PROT_WRITE,
+		    MAP_ANON | MAP_PRIVATE | MAP_FIXED, -1, 0);
+	ASSERT_NE(ptr2, MAP_FAILED);
+	ASSERT_TRUE(find_vma_procmap(procmap, ptr));
+	ASSERT_EQ(procmap->query.vma_start, (unsigned long)ptr);
+	ASSERT_EQ(procmap->query.vma_end, (unsigned long)ptr + 2 * page_size);
+}
+
 TEST_HARNESS_MAIN
-- 
2.49.0