Base
====
This series is based on top of my series which adds minor fault handling for
hugetlbfs [1]. (And, therefore, it is based on 5.12-rc1 and Peter Xu's series
for disabling huge pmd sharing as well.)
[1] https://lore.kernel.org/linux-fsdevel/[email protected]/T/#t
Changelog
=========
v1->v2:
- For UFFDIO_CONTINUE, don't mess with page flags. Just use find_lock_page to
get a locked page from the page cache, instead of doing __SetPageLocked.
This fixes a VM_BUG_ON v1 hit when handling minor faults for THP-backed
shmem (a tmpfs mounted with huge=always).
Overview
========
See my original series linked above for a detailed overview of minor fault
handling in general. The feature in this series works exactly like the
hugetblfs version (from userspace's perspective).
I'm sending this as a separate series because:
- The original minor fault handling series has a full set of R-Bs, and seems
close to being merged. So, it seems reasonable to start looking at this next
step, which extends the basic functionality.
- shmem is different enough that this series may require some additional work
before it's ready, and I don't want to delay the original series
unnecessarily by bundling them together.
Use Case
========
In some cases it is useful to have VM memory backed by tmpfs instead of
hugetlbfs. So, this feature will be used to support the same VM live migration
use case described in my original series.
Additionally, Android folks (Lokesh Gidra <[email protected]>) hope to
optimize the Android Runtime garbage collector using this feature:
"The plan is to use userfaultfd for concurrently compacting the heap. With
this feature, the heap can be shared-mapped at another location where the
GC-thread(s) could continue the compaction operation without the need to
invoke userfault ioctl(UFFDIO_COPY) each time. OTOH, if and when Java threads
get faults on the heap, UFFDIO_CONTINUE can be used to resume execution.
Furthermore, this feature enables updating references in the 'non-moving'
portion of the heap efficiently. Without this feature, uneccessary page
copying (ioctl(UFFDIO_COPY)) would be required."
Axel Rasmussen (5):
userfaultfd: support minor fault handling for shmem
userfaultfd/selftests: use memfd_create for shmem test type
userfaultfd/selftests: create alias mappings in the shmem test
userfaultfd/selftests: reinitialize test context in each test
userfaultfd/selftests: exercise minor fault handling shmem support
fs/userfaultfd.c | 6 +-
include/linux/shmem_fs.h | 26 +-
include/uapi/linux/userfaultfd.h | 4 +-
mm/memory.c | 8 +-
mm/shmem.c | 92 +++----
mm/userfaultfd.c | 27 +-
tools/testing/selftests/vm/userfaultfd.c | 322 +++++++++++++++--------
7 files changed, 295 insertions(+), 190 deletions(-)
--
2.30.1.766.gb4fecdf3b7-goog
Enable test_uffdio_minor for test_type == TEST_SHMEM, and modify the
test slightly to pass in / check for the right feature flags.
Signed-off-by: Axel Rasmussen <[email protected]>
---
tools/testing/selftests/vm/userfaultfd.c | 19 ++++++++++++++-----
1 file changed, 14 insertions(+), 5 deletions(-)
diff --git a/tools/testing/selftests/vm/userfaultfd.c b/tools/testing/selftests/vm/userfaultfd.c
index 5183ddb3080d..f31e9a4edc55 100644
--- a/tools/testing/selftests/vm/userfaultfd.c
+++ b/tools/testing/selftests/vm/userfaultfd.c
@@ -1410,7 +1410,7 @@ static int userfaultfd_minor_test(void)
void *expected_page;
char c;
struct uffd_stats stats = { 0 };
- uint64_t features = UFFD_FEATURE_MINOR_HUGETLBFS;
+ uint64_t req_features, features_out;
if (!test_uffdio_minor)
return 0;
@@ -1418,10 +1418,18 @@ static int userfaultfd_minor_test(void)
printf("testing minor faults: ");
fflush(stdout);
- if (uffd_test_ctx_clear() || uffd_test_ctx_init_ext(&features))
+ if (test_type == TEST_HUGETLB)
+ req_features = UFFD_FEATURE_MINOR_HUGETLBFS;
+ else if (test_type == TEST_SHMEM)
+ req_features = UFFD_FEATURE_MINOR_SHMEM;
+ else
+ return 1;
+
+ features_out = req_features;
+ if (uffd_test_ctx_clear() || uffd_test_ctx_init_ext(&features_out))
return 1;
- /* If kernel reports the feature isn't supported, skip the test. */
- if (!(features & UFFD_FEATURE_MINOR_HUGETLBFS)) {
+ /* If kernel reports required features aren't supported, skip test. */
+ if ((features_out & req_features) != req_features) {
printf("skipping test due to lack of feature support\n");
fflush(stdout);
return 0;
@@ -1431,7 +1439,7 @@ static int userfaultfd_minor_test(void)
uffdio_register.range.len = nr_pages * page_size;
uffdio_register.mode = UFFDIO_REGISTER_MODE_MINOR;
if (ioctl(uffd, UFFDIO_REGISTER, &uffdio_register)) {
- fprintf(stderr, "register failure\n");
+ perror("register failure");
exit(1);
}
@@ -1695,6 +1703,7 @@ static void set_test_type(const char *type)
map_shared = true;
test_type = TEST_SHMEM;
uffd_test_ops = &shmem_uffd_test_ops;
+ test_uffdio_minor = true;
} else {
fprintf(stderr, "Unknown test type: %s\n", type); exit(1);
}
--
2.30.1.766.gb4fecdf3b7-goog