[PATCH v5 0/4] Userspace controls soft-offline pages

[PATCH v5 0/4] Userspace controls soft-offline pages

[Jiaqi Yan]

Correctable memory errors are very common on servers with large
amount of memory, and are corrected by ECC, but with two
pain points to users:
1. Correction usually happens on the fly and adds latency overhead
2. Not-fully-proved theory states excessive correctable memory
   errors can develop into uncorrectable memory error.

Soft offline is kernel's additional solution for memory pages
having (excessive) corrected memory errors. Impacted page is migrated
to healthy page if it is in use, then the original page is discarded
for any future use.

The actual policy on whether (and when) to soft offline should be
maintained by userspace, especially in case of an 1G HugeTLB page.
Soft-offline dissolves the HugeTLB page, either in-use or free, into
chunks of 4K pages, reducing HugeTLB pool capacity by 1 hugepage.
If userspace has not acknowledged such behavior, it may be surprised
when later mmap hugepages MAP_FAILED due to lack of hugepages.
In case of a transparent hugepage, it will be split into 4K pages
as well; userspace will stop enjoying the transparent performance.

In addition, discarding the entire 1G HugeTLB page only because of
corrected memory errors sounds very costly and kernel better not
doing under the hood. But today there are at least 2 such cases:
1. GHES driver sees both GHES_SEV_CORRECTED and
   CPER_SEC_ERROR_THRESHOLD_EXCEEDED after parsing CPER.
2. RAS Correctable Errors Collector counts correctable errors per
   PFN and when the counter for a PFN reaches threshold
In both cases, userspace has no control of the soft offline performed
by kernel's memory failure recovery.

This patch series give userspace the control of softofflining any page:
kernel only soft offlines raw page / transparent hugepage / HugeTLB
hugepage if userspace has agreed to. The interface to userspace is a
new sysctl called enable_soft_offline under /proc/sys/vm. By default
enable_soft_line is 1 to preserve existing behavior in kernel.

Changelog

v4 => v5:
* incorportate feedbacks from Muhammad Usama Anjum
  <usama.anjum@collabora.com>
* refactor selftest to use what available in kselftest.h.
* update a comment in soft_offline_page.

v3 => v4:
* incorporate feedbacks from Miaohe Lin <linmiaohe@huawei.com>,
  Andrew Morton <akpm@linux-foundation.org>, and
  Oscar Salvador <osalvador@suse.de>.
* insert a refactor commit to unify soft offline's logs to follow
  "Soft offline: 0x${pfn}: ${message}" format.
* some rewords in document: fail => will not perform.
* v4 is still based on commit 83a7eefedc9b ("Linux 6.10-rc3"),
  akpm/mm-stable.

v2 => v3:
* incorporate feedbacks from Miaohe Lin <linmiaohe@huawei.com>,
  Lance Yang <ioworker0@gmail.com>, Oscar Salvador <osalvador@suse.de>,
  and David Rientjes <rientjes@google.com>.
* release potential refcount if enable_soft_offline is 0.
* soft_offline_page() returns EOPNOTSUPP if enable_soft_offline is 0.
* refactor hugetlb-soft-offline.c, for example, introduce
  test_soft_offline_common to reduce repeated code.
* rewrite enable_soft_offline's documentation, adds more details about
  the cost of soft-offline for transparent and hugetlb hugepages, and
  components that are impacted when enable_soft_offline becomes 0.
* fix typos in commit messages.
* v3 is still based on commit 83a7eefedc9b ("Linux 6.10-rc3").

v1 => v2:
* incorporate feedbacks from both Miaohe Lin <linmiaohe@huawei.com> and
  Jane Chu <jane.chu@oracle.com>.
* make the switch to control all pages, instead of HugeTLB specific.
* change the API from
  /sys/kernel/mm/hugepages/hugepages-${size}kB/softoffline_corrected_errors
  to /proc/sys/vm/enable_soft_offline.
* minor update to test code.
* update documentation of the user control API.
* v2 is based on commit 83a7eefedc9b ("Linux 6.10-rc3").

Jiaqi Yan (4):
  mm/memory-failure: refactor log format in soft offline code
  mm/memory-failure: userspace controls soft-offlining pages
  selftest/mm: test enable_soft_offline behaviors
  docs: mm: add enable_soft_offline sysctl

 Documentation/admin-guide/sysctl/vm.rst       |  32 +++
 mm/memory-failure.c                           |  38 ++-
 tools/testing/selftests/mm/.gitignore         |   1 +
 tools/testing/selftests/mm/Makefile           |   1 +
 .../selftests/mm/hugetlb-soft-offline.c       | 227 ++++++++++++++++++
 tools/testing/selftests/mm/run_vmtests.sh     |   4 +
 6 files changed, 295 insertions(+), 8 deletions(-)
 create mode 100644 tools/testing/selftests/mm/hugetlb-soft-offline.c

-- 
2.45.2.741.gdbec12cfda-goog

[PATCH v5 1/4] mm/memory-failure: refactor log format in soft offline code

[Jiaqi Yan]

Logs from soft_offline_page and soft_offline_in_use_page have
different formats than majority of the memory failure code:

  "Memory failure: 0x${pfn}: ${lower_case_message}"

Convert them to the following format:

  "Soft offline: 0x${pfn}: ${lower_case_message}"

No functional change in this commit.

Signed-off-by: Jiaqi Yan <jiaqiyan@google.com>
---
 mm/memory-failure.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index d3c830e817e3..2a097af7da0e 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -2631,6 +2631,9 @@ int unpoison_memory(unsigned long pfn)
 }
 EXPORT_SYMBOL(unpoison_memory);
 
+#undef pr_fmt
+#define pr_fmt(fmt) "Soft offline: " fmt
+
 static bool mf_isolate_folio(struct folio *folio, struct list_head *pagelist)
 {
 	bool isolated = false;
@@ -2686,7 +2689,7 @@ static int soft_offline_in_use_page(struct page *page)
 
 	if (!huge && folio_test_large(folio)) {
 		if (try_to_split_thp_page(page)) {
-			pr_info("soft offline: %#lx: thp split failed\n", pfn);
+			pr_info("%#lx: thp split failed\n", pfn);
 			return -EBUSY;
 		}
 		folio = page_folio(page);
@@ -2698,7 +2701,7 @@ static int soft_offline_in_use_page(struct page *page)
 	if (PageHWPoison(page)) {
 		folio_unlock(folio);
 		folio_put(folio);
-		pr_info("soft offline: %#lx page already poisoned\n", pfn);
+		pr_info("%#lx page already poisoned\n", pfn);
 		return 0;
 	}
 
@@ -2711,7 +2714,7 @@ static int soft_offline_in_use_page(struct page *page)
 	folio_unlock(folio);
 
 	if (ret) {
-		pr_info("soft_offline: %#lx: invalidated\n", pfn);
+		pr_info("%#lx: invalidated\n", pfn);
 		page_handle_poison(page, false, true);
 		return 0;
 	}
@@ -2728,13 +2731,13 @@ static int soft_offline_in_use_page(struct page *page)
 			if (!list_empty(&pagelist))
 				putback_movable_pages(&pagelist);
 
-			pr_info("soft offline: %#lx: %s migration failed %ld, type %pGp\n",
+			pr_info("%#lx: %s migration failed %ld, type %pGp\n",
 				pfn, msg_page[huge], ret, &page->flags);
 			if (ret > 0)
 				ret = -EBUSY;
 		}
 	} else {
-		pr_info("soft offline: %#lx: %s isolation failed, page count %d, type %pGp\n",
+		pr_info("%#lx: %s isolation failed, page count %d, type %pGp\n",
 			pfn, msg_page[huge], page_count(page), &page->flags);
 		ret = -EBUSY;
 	}
@@ -2786,7 +2789,7 @@ int soft_offline_page(unsigned long pfn, int flags)
 	mutex_lock(&mf_mutex);
 
 	if (PageHWPoison(page)) {
-		pr_info("%s: %#lx page already poisoned\n", __func__, pfn);
+		pr_info("%#lx: page already poisoned\n", pfn);
 		put_ref_page(pfn, flags);
 		mutex_unlock(&mf_mutex);
 		return 0;
-- 
2.45.2.741.gdbec12cfda-goog

[PATCH v5 2/4] mm/memory-failure: userspace controls soft-offlining pages

[Jiaqi Yan]

Correctable memory errors are very common on servers with large
amount of memory, and are corrected by ECC. Soft offline is kernel's
additional recovery handling for memory pages having (excessive)
corrected memory errors. Impacted page is migrated to a healthy page
if inuse; the original page is discarded for any future use.

The actual policy on whether (and when) to soft offline should be
maintained by userspace, especially in case of an 1G HugeTLB page.
Soft-offline dissolves the HugeTLB page, either in-use or free, into
chunks of 4K pages, reducing HugeTLB pool capacity by 1 hugepage.
If userspace has not acknowledged such behavior, it may be surprised
when later failed to mmap hugepages due to lack of hugepages.
In case of a transparent hugepage, it will be split into 4K pages
as well; userspace will stop enjoying the transparent performance.

In addition, discarding the entire 1G HugeTLB page only because of
corrected memory errors sounds very costly and kernel better not
doing under the hood. But today there are at least 2 such cases
doing so:
1. when GHES driver sees both GHES_SEV_CORRECTED and
   CPER_SEC_ERROR_THRESHOLD_EXCEEDED after parsing CPER.
2. RAS Correctable Errors Collector counts correctable errors per
   PFN and when the counter for a PFN reaches threshold
In both cases, userspace has no control of the soft offline performed
by kernel's memory failure recovery.

This commit gives userspace the control of softofflining any page:
kernel only soft offlines raw page / transparent hugepage / HugeTLB
hugepage if userspace has agreed to. The interface to userspace is a
new sysctl at /proc/sys/vm/enable_soft_offline. By default its value
is set to 1 to preserve existing behavior in kernel. When set to 0,
soft-offline (e.g. MADV_SOFT_OFFLINE) will fail with EOPNOTSUPP.

Acked-by: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Jiaqi Yan <jiaqiyan@google.com>
---
 mm/memory-failure.c | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 2a097af7da0e..0013d338569b 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -68,6 +68,8 @@ static int sysctl_memory_failure_early_kill __read_mostly;
 
 static int sysctl_memory_failure_recovery __read_mostly = 1;
 
+static int sysctl_enable_soft_offline __read_mostly = 1;
+
 atomic_long_t num_poisoned_pages __read_mostly = ATOMIC_LONG_INIT(0);
 
 static bool hw_memory_failure __read_mostly = false;
@@ -141,6 +143,15 @@ static struct ctl_table memory_failure_table[] = {
 		.extra1		= SYSCTL_ZERO,
 		.extra2		= SYSCTL_ONE,
 	},
+	{
+		.procname	= "enable_soft_offline",
+		.data		= &sysctl_enable_soft_offline,
+		.maxlen		= sizeof(sysctl_enable_soft_offline),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= SYSCTL_ZERO,
+		.extra2		= SYSCTL_ONE,
+	}
 };
 
 /*
@@ -2749,8 +2760,9 @@ static int soft_offline_in_use_page(struct page *page)
  * @pfn: pfn to soft-offline
  * @flags: flags. Same as memory_failure().
  *
- * Returns 0 on success
- *         -EOPNOTSUPP for hwpoison_filter() filtered the error event
+ * Returns 0 on success,
+ *         -EOPNOTSUPP for hwpoison_filter() filtered the error event, or
+ *         disabled by /proc/sys/vm/enable_soft_offline,
  *         < 0 otherwise negated errno.
  *
  * Soft offline a page, by migration or invalidation,
@@ -2786,6 +2798,13 @@ int soft_offline_page(unsigned long pfn, int flags)
 		return -EIO;
 	}
 
+	if (!sysctl_enable_soft_offline) {
+		pr_info_once("%#lx: disabled by /proc/sys/vm/enable_soft_offline\n",
+			pfn);
+		put_ref_page(pfn, flags);
+		return -EOPNOTSUPP;
+	}
+
 	mutex_lock(&mf_mutex);
 
 	if (PageHWPoison(page)) {
-- 
2.45.2.741.gdbec12cfda-goog

[PATCH v5 3/4] selftest/mm: test enable_soft_offline behaviors

[Jiaqi Yan]

Add regression and new tests when hugepage has correctable memory
errors, and how userspace wants to deal with it:
* if enable_soft_offline=1, mapped hugepage is soft offlined
* if enable_soft_offline=0, mapped hugepage is intact

Free hugepages case is not explicitly covered by the tests.

Hugepage having corrected memory errors is emulated with
MADV_SOFT_OFFLINE.

Signed-off-by: Jiaqi Yan <jiaqiyan@google.com>
---
 tools/testing/selftests/mm/.gitignore         |   1 +
 tools/testing/selftests/mm/Makefile           |   1 +
 .../selftests/mm/hugetlb-soft-offline.c       | 227 ++++++++++++++++++
 tools/testing/selftests/mm/run_vmtests.sh     |   4 +
 4 files changed, 233 insertions(+)
 create mode 100644 tools/testing/selftests/mm/hugetlb-soft-offline.c

diff --git a/tools/testing/selftests/mm/.gitignore b/tools/testing/selftests/mm/.gitignore
index 0b9ab987601c..064e7b125643 100644
--- a/tools/testing/selftests/mm/.gitignore
+++ b/tools/testing/selftests/mm/.gitignore
@@ -6,6 +6,7 @@ hugepage-shm
 hugepage-vmemmap
 hugetlb-madvise
 hugetlb-read-hwpoison
+hugetlb-soft-offline
 khugepaged
 map_hugetlb
 map_populate
diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
index 3b49bc3d0a3b..d166067d75ef 100644
--- a/tools/testing/selftests/mm/Makefile
+++ b/tools/testing/selftests/mm/Makefile
@@ -42,6 +42,7 @@ TEST_GEN_FILES += gup_test
 TEST_GEN_FILES += hmm-tests
 TEST_GEN_FILES += hugetlb-madvise
 TEST_GEN_FILES += hugetlb-read-hwpoison
+TEST_GEN_FILES += hugetlb-soft-offline
 TEST_GEN_FILES += hugepage-mmap
 TEST_GEN_FILES += hugepage-mremap
 TEST_GEN_FILES += hugepage-shm
diff --git a/tools/testing/selftests/mm/hugetlb-soft-offline.c b/tools/testing/selftests/mm/hugetlb-soft-offline.c
new file mode 100644
index 000000000000..16fe52f972e2
--- /dev/null
+++ b/tools/testing/selftests/mm/hugetlb-soft-offline.c
@@ -0,0 +1,227 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Test soft offline behavior for HugeTLB pages:
+ * - if enable_soft_offline = 0, hugepages should stay intact and soft
+ *   offlining failed with EINVAL.
+ * - if enable_soft_offline = 1, a hugepage should be dissolved and
+ *   nr_hugepages/free_hugepages should be reduced by 1.
+ *
+ * Before running, make sure more than 2 hugepages of default_hugepagesz
+ * are allocated. For example, if /proc/meminfo/Hugepagesize is 2048kB:
+ *   echo 8 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
+ */
+
+#define _GNU_SOURCE
+#include <errno.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+#include <linux/magic.h>
+#include <linux/memfd.h>
+#include <sys/mman.h>
+#include <sys/statfs.h>
+#include <sys/types.h>
+
+#include "../kselftest.h"
+
+#ifndef MADV_SOFT_OFFLINE
+#define MADV_SOFT_OFFLINE 101
+#endif
+
+#define EPREFIX " !!! "
+
+static int do_soft_offline(int fd, size_t len, int expect_errno)
+{
+	char *filemap = NULL;
+	char *hwp_addr = NULL;
+	const unsigned long pagesize = getpagesize();
+	int ret = 0;
+
+	if (ftruncate(fd, len) < 0) {
+		ksft_perror(EPREFIX "ftruncate to len failed");
+		return -1;
+	}
+
+	filemap = mmap(NULL, len, PROT_READ | PROT_WRITE,
+		       MAP_SHARED | MAP_POPULATE, fd, 0);
+	if (filemap == MAP_FAILED) {
+		ksft_perror(EPREFIX "mmap failed");
+		ret = -1;
+		goto untruncate;
+	}
+
+	memset(filemap, 0xab, len);
+	ksft_print_msg("Allocated %#lx bytes of hugetlb pages\n", len);
+
+	hwp_addr = filemap + len / 2;
+	ret = madvise(hwp_addr, pagesize, MADV_SOFT_OFFLINE);
+	ksft_print_msg("MADV_SOFT_OFFLINE %p ret=%d, errno=%d\n",
+		       hwp_addr, ret, errno);
+	if (ret != 0)
+		ksft_perror(EPREFIX "madvise failed");
+
+	if (errno == expect_errno)
+		ret = 0;
+	else {
+		ksft_print_msg("MADV_SOFT_OFFLINE should ret %d\n",
+			       expect_errno);
+		ret = -1;
+	}
+
+	munmap(filemap, len);
+untruncate:
+	if (ftruncate(fd, 0) < 0)
+		ksft_perror(EPREFIX "ftruncate back to 0 failed");
+
+	return ret;
+}
+
+static int set_enable_soft_offline(int value)
+{
+	char cmd[256] = {0};
+	FILE *cmdfile = NULL;
+
+	if (value != 0 && value != 1)
+		return -EINVAL;
+
+	sprintf(cmd, "echo %d > /proc/sys/vm/enable_soft_offline", value);
+	cmdfile = popen(cmd, "r");
+
+	if (cmdfile)
+		ksft_print_msg("enable_soft_offline => %d\n", value);
+	else {
+		ksft_perror(EPREFIX "failed to set enable_soft_offline");
+		return errno;
+	}
+
+	pclose(cmdfile);
+	return 0;
+}
+
+static int read_nr_hugepages(unsigned long hugepage_size,
+			     unsigned long *nr_hugepages)
+{
+	char buffer[256] = {0};
+	char cmd[256] = {0};
+
+	sprintf(cmd, "cat /sys/kernel/mm/hugepages/hugepages-%ldkB/nr_hugepages",
+		hugepage_size);
+	FILE *cmdfile = popen(cmd, "r");
+
+	if (cmdfile == NULL) {
+		ksft_perror(EPREFIX "failed to popen nr_hugepages");
+		return -1;
+	}
+
+	if (!fgets(buffer, sizeof(buffer), cmdfile)) {
+		ksft_perror(EPREFIX "failed to read nr_hugepages");
+		pclose(cmdfile);
+		return -1;
+	}
+
+	*nr_hugepages = atoll(buffer);
+	pclose(cmdfile);
+	return 0;
+}
+
+static int create_hugetlbfs_file(struct statfs *file_stat)
+{
+	int fd;
+
+	fd = memfd_create("hugetlb_tmp", MFD_HUGETLB);
+	if (fd < 0) {
+		ksft_perror(EPREFIX "could not open hugetlbfs file");
+		return -1;
+	}
+
+	memset(file_stat, 0, sizeof(*file_stat));
+	if (fstatfs(fd, file_stat)) {
+		ksft_perror(EPREFIX "fstatfs failed");
+		goto close;
+	}
+	if (file_stat->f_type != HUGETLBFS_MAGIC) {
+		ksft_print_msg(EPREFIX "not hugetlbfs file\n");
+		goto close;
+	}
+
+	return fd;
+close:
+	close(fd);
+	return -1;
+}
+
+static void test_soft_offline_common(int enable_soft_offline)
+{
+	int fd;
+	int expect_errno = enable_soft_offline ? 0 : EOPNOTSUPP;
+	struct statfs file_stat;
+	unsigned long hugepagesize_kb = 0;
+	unsigned long nr_hugepages_before = 0;
+	unsigned long nr_hugepages_after = 0;
+	int ret;
+
+	ksft_print_msg("Test soft-offline when enabled_soft_offline=%d\n",
+		       enable_soft_offline);
+
+	fd = create_hugetlbfs_file(&file_stat);
+	if (fd < 0) {
+		ksft_exit_fail_msg("Failed to create hugetlbfs file\n");
+		return;
+	}
+
+	hugepagesize_kb = file_stat.f_bsize / 1024;
+	ksft_print_msg("Hugepagesize is %ldkB\n", hugepagesize_kb);
+
+	if (set_enable_soft_offline(enable_soft_offline)) {
+		ksft_exit_fail_msg("Failed to set enable_soft_offline\n");
+		return;
+	}
+
+	if (read_nr_hugepages(hugepagesize_kb, &nr_hugepages_before) != 0) {
+		ksft_exit_fail_msg("Failed to read nr_hugepages\n");
+		return;
+	}
+
+	ksft_print_msg("Before MADV_SOFT_OFFLINE nr_hugepages=%ld\n",
+		       nr_hugepages_before);
+
+	ret = do_soft_offline(fd, 2 * file_stat.f_bsize, expect_errno);
+
+	if (read_nr_hugepages(hugepagesize_kb, &nr_hugepages_after) != 0) {
+		ksft_exit_fail_msg("Failed to read nr_hugepages\n");
+		return;
+	}
+
+	ksft_print_msg("After MADV_SOFT_OFFLINE nr_hugepages=%ld\n",
+		nr_hugepages_after);
+
+	if (enable_soft_offline) {
+		if (nr_hugepages_before != nr_hugepages_after + 1) {
+			ksft_test_result_fail("MADV_SOFT_OFFLINE should reduced 1 hugepage\n");
+			return;
+		}
+	} else {
+		if (nr_hugepages_before != nr_hugepages_after) {
+			ksft_test_result_fail("MADV_SOFT_OFFLINE reduced %lu hugepages\n",
+				nr_hugepages_before - nr_hugepages_after);
+			return;
+		}
+	}
+
+	ksft_test_result(ret == 0,
+			 "Test soft-offline when enabled_soft_offline=%d\n",
+			 enable_soft_offline);
+}
+
+int main(int argc, char **argv)
+{
+	ksft_print_header();
+	ksft_set_plan(2);
+
+	test_soft_offline_common(1);
+	test_soft_offline_common(0);
+
+	ksft_finished();
+}
diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh
index 3157204b9047..781117fac1ba 100755
--- a/tools/testing/selftests/mm/run_vmtests.sh
+++ b/tools/testing/selftests/mm/run_vmtests.sh
@@ -331,6 +331,10 @@ CATEGORY="hugetlb" run_test ./thuge-gen
 CATEGORY="hugetlb" run_test ./charge_reserved_hugetlb.sh -cgroup-v2
 CATEGORY="hugetlb" run_test ./hugetlb_reparenting_test.sh -cgroup-v2
 if $RUN_DESTRUCTIVE; then
+nr_hugepages_tmp=$(cat /proc/sys/vm/nr_hugepages)
+echo 8 > /proc/sys/vm/nr_hugepages
+CATEGORY="hugetlb" run_test ./hugetlb-soft-offline
+echo "$nr_hugepages_tmp" > /proc/sys/vm/nr_hugepages
 CATEGORY="hugetlb" run_test ./hugetlb-read-hwpoison
 fi
 
-- 
2.45.2.741.gdbec12cfda-goog

[PATCH v5 4/4] docs: mm: add enable_soft_offline sysctl

[Jiaqi Yan]

Add the documentation for soft offline behaviors / costs, and what
the new enable_soft_offline sysctl is for.

Acked-by: Oscar Salvador <osalvador@suse.de>

Signed-off-by: Jiaqi Yan <jiaqiyan@google.com>
---
 Documentation/admin-guide/sysctl/vm.rst | 32 +++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst
index e86c968a7a0e..71463a7b3e2a 100644
--- a/Documentation/admin-guide/sysctl/vm.rst
+++ b/Documentation/admin-guide/sysctl/vm.rst
@@ -36,6 +36,7 @@ Currently, these files are in /proc/sys/vm:
 - dirtytime_expire_seconds
 - dirty_writeback_centisecs
 - drop_caches
+- enable_soft_offline
 - extfrag_threshold
 - highmem_is_dirtyable
 - hugetlb_shm_group
@@ -267,6 +268,37 @@ used::
 These are informational only.  They do not mean that anything is wrong
 with your system.  To disable them, echo 4 (bit 2) into drop_caches.
 
+enable_soft_offline
+===================
+Correctable memory errors are very common on servers. Soft-offline is kernel's
+solution for memory pages having (excessive) corrected memory errors.
+
+For different types of page, soft-offline has different behaviors / costs.
+- For a raw error page, soft-offline migrates the in-use page's content to
+  a new raw page.
+- For a page that is part of a transparent hugepage,  soft-offline splits the
+  transparent hugepage into raw pages, then migrates only the raw error page.
+  As a result, user is transparently backed by 1 less hugepage, impacting
+  memory access performance.
+- For a page that is part of a HugeTLB hugepage, soft-offline first migrates
+  the entire HugeTLB hugepage, during which a free hugepage will be consumed
+  as migration target.  Then the original hugepage is dissolved into raw
+  pages without compensation, reducing the capacity of the HugeTLB pool by 1.
+
+It is user's call to choose between reliability (staying away from fragile
+physical memory) vs performance / capacity implications in transparent and
+HugeTLB cases.
+
+For all architectures, enable_soft_offline controls whether to soft offline
+memory pages.  When setting to 1, kernel attempts to soft offline the pages
+whenever it thinks needed.  When setting to 0, kernel returns EOPNOTSUPP to
+the request to soft offline the pages.  Its default value is 1.
+
+It is worth mentioning that after setting enable_soft_offline to 0, the
+following requests to soft offline pages will not be performed:
+- Request to soft offline pages from RAS Correctable Errors Collector.
+- On ARM, the request to soft offline pages from GHES driver.
+- On PARISC, the request to soft offline pages from Page Deallocation Table.
 
 extfrag_threshold
 =================
-- 
2.45.2.741.gdbec12cfda-goog

Re: [PATCH v5 1/4] mm/memory-failure: refactor log format in soft offline code

[Miaohe Lin]

On 2024/6/25 0:33, Jiaqi Yan wrote:
> Logs from soft_offline_page and soft_offline_in_use_page have
> different formats than majority of the memory failure code:
> 
>   "Memory failure: 0x${pfn}: ${lower_case_message}"
> 
> Convert them to the following format:
> 
>   "Soft offline: 0x${pfn}: ${lower_case_message}"
> 
> No functional change in this commit.
> 
> Signed-off-by: Jiaqi Yan <jiaqiyan@google.com>
> ---
>  mm/memory-failure.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index d3c830e817e3..2a097af7da0e 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -2631,6 +2631,9 @@ int unpoison_memory(unsigned long pfn)
>  }
>  EXPORT_SYMBOL(unpoison_memory);
>  
> +#undef pr_fmt
> +#define pr_fmt(fmt) "Soft offline: " fmt
> +
>  static bool mf_isolate_folio(struct folio *folio, struct list_head *pagelist)
>  {
>  	bool isolated = false;
> @@ -2686,7 +2689,7 @@ static int soft_offline_in_use_page(struct page *page)
>  
>  	if (!huge && folio_test_large(folio)) {
>  		if (try_to_split_thp_page(page)) {
> -			pr_info("soft offline: %#lx: thp split failed\n", pfn);
> +			pr_info("%#lx: thp split failed\n", pfn);
>  			return -EBUSY;
>  		}
>  		folio = page_folio(page);
> @@ -2698,7 +2701,7 @@ static int soft_offline_in_use_page(struct page *page)
>  	if (PageHWPoison(page)) {
>  		folio_unlock(folio);
>  		folio_put(folio);
> -		pr_info("soft offline: %#lx page already poisoned\n", pfn);
> +		pr_info("%#lx page already poisoned\n", pfn);

Again, it's better to be "%#lx: page" to make log format consistent.
Thanks.
.

Re: [PATCH v5 3/4] selftest/mm: test enable_soft_offline behaviors

[Miaohe Lin]

On 2024/6/25 0:33, Jiaqi Yan wrote:
> Add regression and new tests when hugepage has correctable memory
...
> diff --git a/tools/testing/selftests/mm/hugetlb-soft-offline.c b/tools/testing/selftests/mm/hugetlb-soft-offline.c
> new file mode 100644
> index 000000000000..16fe52f972e2
> --- /dev/null
> +++ b/tools/testing/selftests/mm/hugetlb-soft-offline.c
> @@ -0,0 +1,227 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Test soft offline behavior for HugeTLB pages:
> + * - if enable_soft_offline = 0, hugepages should stay intact and soft
> + *   offlining failed with EINVAL.

s/failed with EINVAL/failed with EOPNOTSUPP/g

> + * - if enable_soft_offline = 1, a hugepage should be dissolved and
> + *   nr_hugepages/free_hugepages should be reduced by 1.
> + *
> + * Before running, make sure more than 2 hugepages of default_hugepagesz
> + * are allocated. For example, if /proc/meminfo/Hugepagesize is 2048kB:
> + *   echo 8 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
> + */
> +
...
> +static void test_soft_offline_common(int enable_soft_offline)
> +{
> +	int fd;
> +	int expect_errno = enable_soft_offline ? 0 : EOPNOTSUPP;
> +	struct statfs file_stat;
> +	unsigned long hugepagesize_kb = 0;
> +	unsigned long nr_hugepages_before = 0;
> +	unsigned long nr_hugepages_after = 0;
> +	int ret;
> +
> +	ksft_print_msg("Test soft-offline when enabled_soft_offline=%d\n",
> +		       enable_soft_offline);
> +
> +	fd = create_hugetlbfs_file(&file_stat);
> +	if (fd < 0) {
> +		ksft_exit_fail_msg("Failed to create hugetlbfs file\n");
> +		return;
> +	}
> +
> +	hugepagesize_kb = file_stat.f_bsize / 1024;
> +	ksft_print_msg("Hugepagesize is %ldkB\n", hugepagesize_kb);
> +
> +	if (set_enable_soft_offline(enable_soft_offline)) {
> +		ksft_exit_fail_msg("Failed to set enable_soft_offline\n");

Call destroy_hugetlbfs_file() in error path?

> +		return;
> +	}
> +
> +	if (read_nr_hugepages(hugepagesize_kb, &nr_hugepages_before) != 0) {
> +		ksft_exit_fail_msg("Failed to read nr_hugepages\n");
> +		return;
> +	}
> +
> +	ksft_print_msg("Before MADV_SOFT_OFFLINE nr_hugepages=%ld\n",
> +		       nr_hugepages_before);
> +
> +	ret = do_soft_offline(fd, 2 * file_stat.f_bsize, expect_errno);
> +
> +	if (read_nr_hugepages(hugepagesize_kb, &nr_hugepages_after) != 0) {
> +		ksft_exit_fail_msg("Failed to read nr_hugepages\n");
> +		return;
> +	}
> +
> +	ksft_print_msg("After MADV_SOFT_OFFLINE nr_hugepages=%ld\n",
> +		nr_hugepages_after);
> +
> +	if (enable_soft_offline) {
> +		if (nr_hugepages_before != nr_hugepages_after + 1) {
> +			ksft_test_result_fail("MADV_SOFT_OFFLINE should reduced 1 hugepage\n");
> +			return;
> +		}
> +	} else {
> +		if (nr_hugepages_before != nr_hugepages_after) {
> +			ksft_test_result_fail("MADV_SOFT_OFFLINE reduced %lu hugepages\n",
> +				nr_hugepages_before - nr_hugepages_after);
> +			return;
> +		}
> +	}
> +
> +	ksft_test_result(ret == 0,
> +			 "Test soft-offline when enabled_soft_offline=%d\n",
> +			 enable_soft_offline);

Call destroy_hugetlbfs_file() when test finished ?

Thanks.
.

Re: [PATCH v5 4/4] docs: mm: add enable_soft_offline sysctl

[Miaohe Lin]

On 2024/6/25 0:33, Jiaqi Yan wrote:
> Add the documentation for soft offline behaviors / costs, and what
> the new enable_soft_offline sysctl is for.
> 
> Acked-by: Oscar Salvador <osalvador@suse.de>
> 
> Signed-off-by: Jiaqi Yan <jiaqiyan@google.com>
> ---
>  Documentation/admin-guide/sysctl/vm.rst | 32 +++++++++++++++++++++++++
>  1 file changed, 32 insertions(+)

LGTM. Thanks.
Acked-by: Miaohe Lin <linmiaohe@huawei.com>
Thanks.
.

Re: [PATCH v5 1/4] mm/memory-failure: refactor log format in soft offline code

[Jiaqi Yan]

On Mon, Jun 24, 2024 at 11:41 PM Miaohe Lin <linmiaohe@huawei.com> wrote:
>
> On 2024/6/25 0:33, Jiaqi Yan wrote:
> > Logs from soft_offline_page and soft_offline_in_use_page have
> > different formats than majority of the memory failure code:
> >
> >   "Memory failure: 0x${pfn}: ${lower_case_message}"
> >
> > Convert them to the following format:
> >
> >   "Soft offline: 0x${pfn}: ${lower_case_message}"
> >
> > No functional change in this commit.
> >
> > Signed-off-by: Jiaqi Yan <jiaqiyan@google.com>
> > ---
> >  mm/memory-failure.c | 15 +++++++++------
> >  1 file changed, 9 insertions(+), 6 deletions(-)
> >
> > diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> > index d3c830e817e3..2a097af7da0e 100644
> > --- a/mm/memory-failure.c
> > +++ b/mm/memory-failure.c
> > @@ -2631,6 +2631,9 @@ int unpoison_memory(unsigned long pfn)
> >  }
> >  EXPORT_SYMBOL(unpoison_memory);
> >
> > +#undef pr_fmt
> > +#define pr_fmt(fmt) "Soft offline: " fmt
> > +
> >  static bool mf_isolate_folio(struct folio *folio, struct list_head *pagelist)
> >  {
> >       bool isolated = false;
> > @@ -2686,7 +2689,7 @@ static int soft_offline_in_use_page(struct page *page)
> >
> >       if (!huge && folio_test_large(folio)) {
> >               if (try_to_split_thp_page(page)) {
> > -                     pr_info("soft offline: %#lx: thp split failed\n", pfn);
> > +                     pr_info("%#lx: thp split failed\n", pfn);
> >                       return -EBUSY;
> >               }
> >               folio = page_folio(page);
> > @@ -2698,7 +2701,7 @@ static int soft_offline_in_use_page(struct page *page)
> >       if (PageHWPoison(page)) {
> >               folio_unlock(folio);
> >               folio_put(folio);
> > -             pr_info("soft offline: %#lx page already poisoned\n", pfn);
> > +             pr_info("%#lx page already poisoned\n", pfn);
>
> Again, it's better to be "%#lx: page" to make log format consistent.

Ah, I missed a ":", thanks for catching this!

> Thanks.
> .

Re: [PATCH v5 4/4] docs: mm: add enable_soft_offline sysctl

[Randy Dunlap]

Hi--

On 6/24/24 9:33 AM, Jiaqi Yan wrote:
> Add the documentation for soft offline behaviors / costs, and what
> the new enable_soft_offline sysctl is for.
> 
> Acked-by: Oscar Salvador <osalvador@suse.de>
> 
> Signed-off-by: Jiaqi Yan <jiaqiyan@google.com>
> ---
>  Documentation/admin-guide/sysctl/vm.rst | 32 +++++++++++++++++++++++++
>  1 file changed, 32 insertions(+)
> 
> diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst
> index e86c968a7a0e..71463a7b3e2a 100644
> --- a/Documentation/admin-guide/sysctl/vm.rst
> +++ b/Documentation/admin-guide/sysctl/vm.rst
> @@ -267,6 +268,37 @@ used::
>  These are informational only.  They do not mean that anything is wrong
>  with your system.  To disable them, echo 4 (bit 2) into drop_caches.
>  
> +enable_soft_offline
> +===================
> +Correctable memory errors are very common on servers. Soft-offline is kernel's
> +solution for memory pages having (excessive) corrected memory errors.
> +
> +For different types of page, soft-offline has different behaviors / costs.
> +- For a raw error page, soft-offline migrates the in-use page's content to
> +  a new raw page.
> +- For a page that is part of a transparent hugepage,  soft-offline splits the

Use only one space after the comma ...................^

> +  transparent hugepage into raw pages, then migrates only the raw error page.
> +  As a result, user is transparently backed by 1 less hugepage, impacting
> +  memory access performance.
> +- For a page that is part of a HugeTLB hugepage, soft-offline first migrates
> +  the entire HugeTLB hugepage, during which a free hugepage will be consumed
> +  as migration target.  Then the original hugepage is dissolved into raw
> +  pages without compensation, reducing the capacity of the HugeTLB pool by 1.
> +
> +It is user's call to choose between reliability (staying away from fragile
> +physical memory) vs performance / capacity implications in transparent and
> +HugeTLB cases.
> +
> +For all architectures, enable_soft_offline controls whether to soft offline
> +memory pages.  When setting to 1, kernel attempts to soft offline the pages

                  When set to 1,

> +whenever it thinks needed.  When setting to 0, kernel returns EOPNOTSUPP to

                               When set to 0,

> +the request to soft offline the pages.  Its default value is 1.
> +
> +It is worth mentioning that after setting enable_soft_offline to 0, the
> +following requests to soft offline pages will not be performed:
> +- Request to soft offline pages from RAS Correctable Errors Collector.
> +- On ARM, the request to soft offline pages from GHES driver.
> +- On PARISC, the request to soft offline pages from Page Deallocation Table.
>  
>  extfrag_threshold
>  =================

-- 
~Randy

Re: [PATCH v5 4/4] docs: mm: add enable_soft_offline sysctl

[Jiaqi Yan]

On Tue, Jun 25, 2024 at 5:02 PM Randy Dunlap <rdunlap@infradead.org> wrote:
>
> Hi--
>
> On 6/24/24 9:33 AM, Jiaqi Yan wrote:
> > Add the documentation for soft offline behaviors / costs, and what
> > the new enable_soft_offline sysctl is for.
> >
> > Acked-by: Oscar Salvador <osalvador@suse.de>
> >
> > Signed-off-by: Jiaqi Yan <jiaqiyan@google.com>
> > ---
> >  Documentation/admin-guide/sysctl/vm.rst | 32 +++++++++++++++++++++++++
> >  1 file changed, 32 insertions(+)
> >
> > diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst
> > index e86c968a7a0e..71463a7b3e2a 100644
> > --- a/Documentation/admin-guide/sysctl/vm.rst
> > +++ b/Documentation/admin-guide/sysctl/vm.rst
> > @@ -267,6 +268,37 @@ used::
> >  These are informational only.  They do not mean that anything is wrong
> >  with your system.  To disable them, echo 4 (bit 2) into drop_caches.
> >
> > +enable_soft_offline
> > +===================
> > +Correctable memory errors are very common on servers. Soft-offline is kernel's
> > +solution for memory pages having (excessive) corrected memory errors.
> > +
> > +For different types of page, soft-offline has different behaviors / costs.
> > +- For a raw error page, soft-offline migrates the in-use page's content to
> > +  a new raw page.
> > +- For a page that is part of a transparent hugepage,  soft-offline splits the
>
> Use only one space after the comma ...................^
>
> > +  transparent hugepage into raw pages, then migrates only the raw error page.
> > +  As a result, user is transparently backed by 1 less hugepage, impacting
> > +  memory access performance.
> > +- For a page that is part of a HugeTLB hugepage, soft-offline first migrates
> > +  the entire HugeTLB hugepage, during which a free hugepage will be consumed
> > +  as migration target.  Then the original hugepage is dissolved into raw
> > +  pages without compensation, reducing the capacity of the HugeTLB pool by 1.
> > +
> > +It is user's call to choose between reliability (staying away from fragile
> > +physical memory) vs performance / capacity implications in transparent and
> > +HugeTLB cases.
> > +
> > +For all architectures, enable_soft_offline controls whether to soft offline
> > +memory pages.  When setting to 1, kernel attempts to soft offline the pages
>
>                   When set to 1,
>
> > +whenever it thinks needed.  When setting to 0, kernel returns EOPNOTSUPP to
>
>                                When set to 0,

Thanks Randy! I will fix these 3 nits in v6.

>
> > +the request to soft offline the pages.  Its default value is 1.
> > +
> > +It is worth mentioning that after setting enable_soft_offline to 0, the
> > +following requests to soft offline pages will not be performed:
> > +- Request to soft offline pages from RAS Correctable Errors Collector.
> > +- On ARM, the request to soft offline pages from GHES driver.
> > +- On PARISC, the request to soft offline pages from Page Deallocation Table.
> >
> >  extfrag_threshold
> >  =================
>
> --
> ~Randy

Re: [PATCH v5 3/4] selftest/mm: test enable_soft_offline behaviors

[Miaohe Lin]

On 2024/6/26 7:57, Jiaqi Yan wrote:
> On Tue, Jun 25, 2024 at 12:05 AM Miaohe Lin <linmiaohe@huawei.com> wrote:
>>
>> On 2024/6/25 0:33, Jiaqi Yan wrote:
>>> Add regression and new tests when hugepage has correctable memory
>> ...
>>> diff --git a/tools/testing/selftests/mm/hugetlb-soft-offline.c b/tools/testing/selftests/mm/hugetlb-soft-offline.c
>>> new file mode 100644
>>> index 000000000000..16fe52f972e2
>>> --- /dev/null
>>> +++ b/tools/testing/selftests/mm/hugetlb-soft-offline.c
>>> @@ -0,0 +1,227 @@
>>> +// SPDX-License-Identifier: GPL-2.0
>>> +/*
>>> + * Test soft offline behavior for HugeTLB pages:
>>> + * - if enable_soft_offline = 0, hugepages should stay intact and soft
>>> + *   offlining failed with EINVAL.
>>
>> s/failed with EINVAL/failed with EOPNOTSUPP/g
> 
> To be fixed in v6.
> 
>>
>>> + * - if enable_soft_offline = 1, a hugepage should be dissolved and
>>> + *   nr_hugepages/free_hugepages should be reduced by 1.
>>> + *
>>> + * Before running, make sure more than 2 hugepages of default_hugepagesz
>>> + * are allocated. For example, if /proc/meminfo/Hugepagesize is 2048kB:
>>> + *   echo 8 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
>>> + */
>>> +
>> ...
>>> +static void test_soft_offline_common(int enable_soft_offline)
>>> +{
>>> +     int fd;
>>> +     int expect_errno = enable_soft_offline ? 0 : EOPNOTSUPP;
>>> +     struct statfs file_stat;
>>> +     unsigned long hugepagesize_kb = 0;
>>> +     unsigned long nr_hugepages_before = 0;
>>> +     unsigned long nr_hugepages_after = 0;
>>> +     int ret;
>>> +
>>> +     ksft_print_msg("Test soft-offline when enabled_soft_offline=%d\n",
>>> +                    enable_soft_offline);
>>> +
>>> +     fd = create_hugetlbfs_file(&file_stat);
>>> +     if (fd < 0) {
>>> +             ksft_exit_fail_msg("Failed to create hugetlbfs file\n");
>>> +             return;
>>> +     }
>>> +
>>> +     hugepagesize_kb = file_stat.f_bsize / 1024;
>>> +     ksft_print_msg("Hugepagesize is %ldkB\n", hugepagesize_kb);
>>> +
>>> +     if (set_enable_soft_offline(enable_soft_offline)) {
>>> +             ksft_exit_fail_msg("Failed to set enable_soft_offline\n");
>>
>> Call destroy_hugetlbfs_file() in error path?
> 
> As the counterpart of destroy_hugetlbfs_file, I think the test only
> needs to close(fd). Will add it in v6.
> 
>>
>>> +             return;
>>> +     }
>>> +
>>> +     if (read_nr_hugepages(hugepagesize_kb, &nr_hugepages_before) != 0) {
>>> +             ksft_exit_fail_msg("Failed to read nr_hugepages\n");
>>> +             return;
>>> +     }
>>> +
>>> +     ksft_print_msg("Before MADV_SOFT_OFFLINE nr_hugepages=%ld\n",
>>> +                    nr_hugepages_before);
>>> +
>>> +     ret = do_soft_offline(fd, 2 * file_stat.f_bsize, expect_errno);
>>> +
>>> +     if (read_nr_hugepages(hugepagesize_kb, &nr_hugepages_after) != 0) {
>>> +             ksft_exit_fail_msg("Failed to read nr_hugepages\n");
>>> +             return;
>>> +     }
>>> +
>>> +     ksft_print_msg("After MADV_SOFT_OFFLINE nr_hugepages=%ld\n",
>>> +             nr_hugepages_after);
>>> +
>>> +     if (enable_soft_offline) {
>>> +             if (nr_hugepages_before != nr_hugepages_after + 1) {
>>> +                     ksft_test_result_fail("MADV_SOFT_OFFLINE should reduced 1 hugepage\n");
>>> +                     return;
>>> +             }
>>> +     } else {
>>> +             if (nr_hugepages_before != nr_hugepages_after) {
>>> +                     ksft_test_result_fail("MADV_SOFT_OFFLINE reduced %lu hugepages\n",
>>> +                             nr_hugepages_before - nr_hugepages_after);
>>> +                     return;
>>> +             }
>>> +     }
>>> +
>>> +     ksft_test_result(ret == 0,
>>> +                      "Test soft-offline when enabled_soft_offline=%d\n",
>>> +                      enable_soft_offline);
>>
>> Call destroy_hugetlbfs_file() when test finished ?
> 
> Test can just close(fd) once nr_hugepages_after is read.

I'm sorry but I can't find the code to call close(fd) after nr_hugepages_after is read.
IMO create_hugetlbfs_file() would fail to create a new hugetlb file later if close(fd)
is not called when testing previous enable_soft_offline = 1 testcase. Because a hugetlb
file with same name is already there. But I might miss something.

Thanks.
.

Re: [PATCH v5 3/4] selftest/mm: test enable_soft_offline behaviors

[Jiaqi Yan]

On Tue, Jun 25, 2024 at 6:54 PM Miaohe Lin <linmiaohe@huawei.com> wrote:
>
> On 2024/6/26 7:57, Jiaqi Yan wrote:
> > On Tue, Jun 25, 2024 at 12:05 AM Miaohe Lin <linmiaohe@huawei.com> wrote:
> >>
> >> On 2024/6/25 0:33, Jiaqi Yan wrote:
> >>> Add regression and new tests when hugepage has correctable memory
> >> ...
> >>> diff --git a/tools/testing/selftests/mm/hugetlb-soft-offline.c b/tools/testing/selftests/mm/hugetlb-soft-offline.c
> >>> new file mode 100644
> >>> index 000000000000..16fe52f972e2
> >>> --- /dev/null
> >>> +++ b/tools/testing/selftests/mm/hugetlb-soft-offline.c
> >>> @@ -0,0 +1,227 @@
> >>> +// SPDX-License-Identifier: GPL-2.0
> >>> +/*
> >>> + * Test soft offline behavior for HugeTLB pages:
> >>> + * - if enable_soft_offline = 0, hugepages should stay intact and soft
> >>> + *   offlining failed with EINVAL.
> >>
> >> s/failed with EINVAL/failed with EOPNOTSUPP/g
> >
> > To be fixed in v6.
> >
> >>
> >>> + * - if enable_soft_offline = 1, a hugepage should be dissolved and
> >>> + *   nr_hugepages/free_hugepages should be reduced by 1.
> >>> + *
> >>> + * Before running, make sure more than 2 hugepages of default_hugepagesz
> >>> + * are allocated. For example, if /proc/meminfo/Hugepagesize is 2048kB:
> >>> + *   echo 8 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
> >>> + */
> >>> +
> >> ...
> >>> +static void test_soft_offline_common(int enable_soft_offline)
> >>> +{
> >>> +     int fd;
> >>> +     int expect_errno = enable_soft_offline ? 0 : EOPNOTSUPP;
> >>> +     struct statfs file_stat;
> >>> +     unsigned long hugepagesize_kb = 0;
> >>> +     unsigned long nr_hugepages_before = 0;
> >>> +     unsigned long nr_hugepages_after = 0;
> >>> +     int ret;
> >>> +
> >>> +     ksft_print_msg("Test soft-offline when enabled_soft_offline=%d\n",
> >>> +                    enable_soft_offline);
> >>> +
> >>> +     fd = create_hugetlbfs_file(&file_stat);
> >>> +     if (fd < 0) {
> >>> +             ksft_exit_fail_msg("Failed to create hugetlbfs file\n");
> >>> +             return;
> >>> +     }
> >>> +
> >>> +     hugepagesize_kb = file_stat.f_bsize / 1024;
> >>> +     ksft_print_msg("Hugepagesize is %ldkB\n", hugepagesize_kb);
> >>> +
> >>> +     if (set_enable_soft_offline(enable_soft_offline)) {
> >>> +             ksft_exit_fail_msg("Failed to set enable_soft_offline\n");
> >>
> >> Call destroy_hugetlbfs_file() in error path?
> >
> > As the counterpart of destroy_hugetlbfs_file, I think the test only
> > needs to close(fd). Will add it in v6.
> >
> >>
> >>> +             return;
> >>> +     }
> >>> +
> >>> +     if (read_nr_hugepages(hugepagesize_kb, &nr_hugepages_before) != 0) {
> >>> +             ksft_exit_fail_msg("Failed to read nr_hugepages\n");
> >>> +             return;
> >>> +     }
> >>> +
> >>> +     ksft_print_msg("Before MADV_SOFT_OFFLINE nr_hugepages=%ld\n",
> >>> +                    nr_hugepages_before);
> >>> +
> >>> +     ret = do_soft_offline(fd, 2 * file_stat.f_bsize, expect_errno);
> >>> +
> >>> +     if (read_nr_hugepages(hugepagesize_kb, &nr_hugepages_after) != 0) {
> >>> +             ksft_exit_fail_msg("Failed to read nr_hugepages\n");
> >>> +             return;
> >>> +     }
> >>> +
> >>> +     ksft_print_msg("After MADV_SOFT_OFFLINE nr_hugepages=%ld\n",
> >>> +             nr_hugepages_after);
> >>> +
> >>> +     if (enable_soft_offline) {
> >>> +             if (nr_hugepages_before != nr_hugepages_after + 1) {
> >>> +                     ksft_test_result_fail("MADV_SOFT_OFFLINE should reduced 1 hugepage\n");
> >>> +                     return;
> >>> +             }
> >>> +     } else {
> >>> +             if (nr_hugepages_before != nr_hugepages_after) {
> >>> +                     ksft_test_result_fail("MADV_SOFT_OFFLINE reduced %lu hugepages\n",
> >>> +                             nr_hugepages_before - nr_hugepages_after);
> >>> +                     return;
> >>> +             }
> >>> +     }
> >>> +
> >>> +     ksft_test_result(ret == 0,
> >>> +                      "Test soft-offline when enabled_soft_offline=%d\n",
> >>> +                      enable_soft_offline);
> >>
> >> Call destroy_hugetlbfs_file() when test finished ?
> >
> > Test can just close(fd) once nr_hugepages_after is read.
>
> I'm sorry but I can't find the code to call close(fd) after nr_hugepages_after is read.

Sorry, I meant in v6 I will add close(fd) after nr_hugepages_after.

> IMO create_hugetlbfs_file() would fail to create a new hugetlb file later if close(fd)
> is not called when testing previous enable_soft_offline = 1 testcase. Because a hugetlb
> file with same name is already there. But I might miss something.

Yes, this is an absolutely valid concern, and should be address in v6
by adding close(fd) after nr_hugepages_after.

>
> Thanks.
> .
>