On Wed, May 21, 2025 at 04:07:29PM +0800, Chengming Zhou wrote:
> On 2025/5/19 16:51, Lorenzo Stoakes wrote:
> > 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@xxxxxxxxxx>
>
> Reviewed-by: Chengming Zhou <chengming.zhou@xxxxxxxxx>
> Tested-by: Chengming Zhou <chengming.zhou@xxxxxxxxx>
Thanks very much! :)
I hope to get a v2 out today, so will carry forward your tags there.
Cheers, Loreno
>
> Thanks!
>
> > ---
> > 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
