[PATCH v4 0/4] Userspace controls soft-offline pages

[PATCH v4 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

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       | 229 ++++++++++++++++++
 tools/testing/selftests/mm/run_vmtests.sh     |   4 +
 6 files changed, 297 insertions(+), 8 deletions(-)
 create mode 100644 tools/testing/selftests/mm/hugetlb-soft-offline.c

-- 
2.45.2.741.gdbec12cfda-goog

[PATCH v4 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 v4 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.

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..623aa93aff5a 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,
+ *         -EOPNOTSUPP if 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 v4 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       | 229 ++++++++++++++++++
 tools/testing/selftests/mm/run_vmtests.sh     |   4 +
 4 files changed, 235 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..5701eea4ee48
--- /dev/null
+++ b/tools/testing/selftests/mm/hugetlb-soft-offline.c
@@ -0,0 +1,229 @@
+// 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>
+
+#ifndef MADV_SOFT_OFFLINE
+#define MADV_SOFT_OFFLINE 101
+#endif
+
+#define PREFIX " ... "
+#define EPREFIX " !!! "
+
+enum test_status {
+	TEST_PASS = 0,
+	TEST_FAILED = 1,
+	// From ${ksft_skip} in run_vmtests.sh.
+	TEST_SKIPPED = 4,
+};
+
+static enum test_status do_soft_offline(int fd, size_t len, int expect_ret)
+{
+	char *filemap = NULL;
+	char *hwp_addr = NULL;
+	const unsigned long pagesize = getpagesize();
+	int ret = 0;
+	enum test_status status = TEST_SKIPPED;
+
+	if (ftruncate(fd, len) < 0) {
+		perror(EPREFIX "ftruncate to len failed");
+		return status;
+	}
+
+	filemap = mmap(NULL, len, PROT_READ | PROT_WRITE,
+		       MAP_SHARED | MAP_POPULATE, fd, 0);
+	if (filemap == MAP_FAILED) {
+		perror(EPREFIX "mmap failed");
+		goto untruncate;
+	}
+
+	memset(filemap, 0xab, len);
+	printf(PREFIX "Allocated %#lx bytes of hugetlb pages\n", len);
+
+	hwp_addr = filemap + len / 2;
+	ret = madvise(hwp_addr, pagesize, MADV_SOFT_OFFLINE);
+	printf(PREFIX "MADV_SOFT_OFFLINE %p ret=%d, errno=%d\n",
+	       hwp_addr, ret, errno);
+	if (ret != 0)
+		perror(EPREFIX "madvise failed");
+
+	if (errno == expect_ret)
+		status = TEST_PASS;
+	else {
+		printf(EPREFIX "MADV_SOFT_OFFLINE should ret %d\n", expect_ret);
+		status = TEST_FAILED;
+	}
+
+	munmap(filemap, len);
+untruncate:
+	if (ftruncate(fd, 0) < 0)
+		perror(EPREFIX "ftruncate back to 0 failed");
+
+	return status;
+}
+
+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)
+		printf(PREFIX "enable_soft_offline => %d\n", value);
+	else {
+		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) {
+		perror(EPREFIX "failed to popen nr_hugepages");
+		return -1;
+	}
+
+	if (!fgets(buffer, sizeof(buffer), cmdfile)) {
+		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) {
+		perror(EPREFIX "could not open hugetlbfs file");
+		return -1;
+	}
+
+	memset(file_stat, 0, sizeof(*file_stat));
+	if (fstatfs(fd, file_stat)) {
+		perror(EPREFIX "fstatfs failed");
+		goto close;
+	}
+	if (file_stat->f_type != HUGETLBFS_MAGIC) {
+		printf(EPREFIX "not hugetlbfs file\n");
+		goto close;
+	}
+
+	return fd;
+close:
+	close(fd);
+	return -1;
+}
+
+static enum test_status test_soft_offline_common(int enable_soft_offline)
+{
+	int fd;
+	int expect_ret = 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;
+	enum test_status status = TEST_SKIPPED;
+
+	printf("Test soft-offline when enabled_soft_offline=%d\n",
+		enable_soft_offline);
+
+	fd = create_hugetlbfs_file(&file_stat);
+	if (fd < 0) {
+		printf(EPREFIX "Failed to create hugetlbfs file\n");
+		return status;
+	}
+
+	hugepagesize_kb = file_stat.f_bsize / 1024;
+	printf(PREFIX "Hugepagesize is %ldkB\n", hugepagesize_kb);
+
+	if (set_enable_soft_offline(enable_soft_offline))
+		return TEST_FAILED;
+
+	if (read_nr_hugepages(hugepagesize_kb, &nr_hugepages_before) != 0)
+		return TEST_FAILED;
+
+	printf(PREFIX "Before MADV_SOFT_OFFLINE nr_hugepages=%ld\n",
+		nr_hugepages_before);
+
+	status = do_soft_offline(fd, 2 * file_stat.f_bsize, expect_ret);
+
+	if (read_nr_hugepages(hugepagesize_kb, &nr_hugepages_after) != 0)
+		return TEST_FAILED;
+
+	printf(PREFIX "After MADV_SOFT_OFFLINE nr_hugepages=%ld\n",
+		nr_hugepages_after);
+
+	if (enable_soft_offline) {
+		if (nr_hugepages_before != nr_hugepages_after + 1) {
+			printf(EPREFIX "MADV_SOFT_OFFLINE should reduced 1 hugepage\n");
+			return TEST_FAILED;
+		}
+	} else {
+		if (nr_hugepages_before != nr_hugepages_after) {
+			printf(EPREFIX "MADV_SOFT_OFFLINE reduced %lu hugepages\n",
+				nr_hugepages_before - nr_hugepages_after);
+			return TEST_FAILED;
+		}
+	}
+
+	return status;
+}
+
+int main(void)
+{
+	enum test_status status;
+
+	status = test_soft_offline_common(1);
+	if (status != TEST_PASS)
+		return status;
+
+	status = test_soft_offline_common(0);
+	if (status != TEST_PASS)
+		return status;
+
+	printf("Soft-offline tests all good!\n");
+	return TEST_PASS;
+}
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 v4 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 v4 0/4] Userspace controls soft-offline pages

[Andi Kleen]

Jiaqi Yan <jiaqiyan@google.com> writes:

> 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.

This patchkit is amusing (or maybe sad) because it basically tries to
reconstruct the original soft offline design using a user space daemon
instead of doing policy badly in the kernel.

You can still have it by enabling CONFIG_X86_MCELOG_LEGACY and
use http://www.mcelog.org or an equivalent daemon of your chosing
that listens to /dev/mcelog.

-Andi

Re: [PATCH v4 3/4] selftest/mm: test enable_soft_offline behaviors

[Muhammad Usama Anjum]

On 6/20/24 11:48 PM, Jiaqi Yan wrote:
> 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       | 229 ++++++++++++++++++
>  tools/testing/selftests/mm/run_vmtests.sh     |   4 +
>  4 files changed, 235 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..5701eea4ee48
> --- /dev/null
> +++ b/tools/testing/selftests/mm/hugetlb-soft-offline.c
> @@ -0,0 +1,229 @@
> +// 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>
> +
> +#ifndef MADV_SOFT_OFFLINE
> +#define MADV_SOFT_OFFLINE 101
> +#endif
> +
> +#define PREFIX " ... "
> +#define EPREFIX " !!! "
> +
> +enum test_status {
> +	TEST_PASS = 0,
> +	TEST_FAILED = 1,
> +	// From ${ksft_skip} in run_vmtests.sh.
> +	TEST_SKIPPED = 4,
> +};
Include ../kselftest.h and use macros from there instead of redifining.
Also try to use helper functions from same header file to mark the test
pass/fail or exit the test entirely. You can look at soft-dirty.c how that
is written.

-- 
BR,
Muhammad Usama Anjum

Re: [PATCH v4 3/4] selftest/mm: test enable_soft_offline behaviors

[Jiaqi Yan]

On Thu, Jun 20, 2024 at 10:08 PM Muhammad Usama Anjum
<usama.anjum@collabora.com> wrote:
>
> On 6/20/24 11:48 PM, Jiaqi Yan wrote:
> > 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       | 229 ++++++++++++++++++
> >  tools/testing/selftests/mm/run_vmtests.sh     |   4 +
> >  4 files changed, 235 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..5701eea4ee48
> > --- /dev/null
> > +++ b/tools/testing/selftests/mm/hugetlb-soft-offline.c
> > @@ -0,0 +1,229 @@
> > +// 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>
> > +
> > +#ifndef MADV_SOFT_OFFLINE
> > +#define MADV_SOFT_OFFLINE 101
> > +#endif
> > +
> > +#define PREFIX " ... "
> > +#define EPREFIX " !!! "
> > +
> > +enum test_status {
> > +     TEST_PASS = 0,
> > +     TEST_FAILED = 1,
> > +     // From ${ksft_skip} in run_vmtests.sh.
> > +     TEST_SKIPPED = 4,
> > +};
> Include ../kselftest.h and use macros from there instead of redifining.
> Also try to use helper functions from same header file to mark the test
> pass/fail or exit the test entirely. You can look at soft-dirty.c how that
> is written.

Thanks Muhammad.

For sure, I will wait a couple of days to see if there is more
feedback on v4, then refactor with kselftest.h in v5.

>
> --
> BR,
> Muhammad Usama Anjum

Re: [PATCH v4 0/4] Userspace controls soft-offline pages

[Jiaqi Yan]

Thanks for your comment, Andi.

On Thu, Jun 20, 2024 at 3:53 PM Andi Kleen <ak@linux.intel.com> wrote:
>
> Jiaqi Yan <jiaqiyan@google.com> writes:
>
> > 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.
>
> This patchkit is amusing (or maybe sad) because it basically tries to
> reconstruct the original soft offline design using a user space daemon
> instead of doing policy badly in the kernel.

Some clarifications. I don't intend to reconstruct. I think this
patchset can also be treated as "patch some missing places so that
kernel doesn't soft offline behind the back of userspace daemon".
I agree with you (IIUC) that the policy for corrected memory errors
should exist in userspace. But the situation is that some behaviors in
the kernel don't respect that (they either have a reason to not
respect, or just forget to respect). enable_soft_offline is basically
the big button in userspace to block these kernel violators.

>
> You can still have it by enabling CONFIG_X86_MCELOG_LEGACY and
> use http://www.mcelog.org or an equivalent daemon of your chosing
> that listens to /dev/mcelog.

If I didn't miss anything important in
https://github.com/andikleen/mcelog and
arch/x86/kernel/cpu/mce/dev-mcelog.c, I don't think /dev/mcelog works
on ARM platforms where CPER is used to convey hw errors from platform
to OS.

In addition, again taking an ARM platform as an example, I don't think
any userspace daemon has the way to stop the GHES driver from soft
offlining memory pages:
https://github.com/torvalds/linux/blob/master/drivers/acpi/apei/ghes.c#L521.
But of course it is not a problem if userspace always wants soft
offline to happen.

>
> -Andi
>
>

Re: [PATCH v4 0/4] Userspace controls soft-offline pages

[Andi Kleen]

On Fri, Jun 21, 2024 at 04:53:41PM -0700, Jiaqi Yan wrote:
> Thanks for your comment, Andi.
> 
> On Thu, Jun 20, 2024 at 3:53 PM Andi Kleen <ak@linux.intel.com> wrote:
> >
> > Jiaqi Yan <jiaqiyan@google.com> writes:
> >
> > > 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.
> >
> > This patchkit is amusing (or maybe sad) because it basically tries to
> > reconstruct the original soft offline design using a user space daemon
> > instead of doing policy badly in the kernel.
> 
> Some clarifications. I don't intend to reconstruct. I think this
> patchset can also be treated as "patch some missing places so that
> kernel doesn't soft offline behind the back of userspace daemon".
> I agree with you (IIUC) that the policy for corrected memory errors
> should exist in userspace. But the situation is that some behaviors in
> the kernel don't respect that (they either have a reason to not
> respect, or just forget to respect). enable_soft_offline is basically
> the big button in userspace to block these kernel violators.

It would be better to disable them earlier before they waste work
tracking things unnecessarily.  But yes it's a step in the right direction.

> 
> >
> > You can still have it by enabling CONFIG_X86_MCELOG_LEGACY and
> > use http://www.mcelog.org or an equivalent daemon of your chosing
> > that listens to /dev/mcelog.
> 
> If I didn't miss anything important in
> https://github.com/andikleen/mcelog and
> arch/x86/kernel/cpu/mce/dev-mcelog.c, I don't think /dev/mcelog works
> on ARM platforms where CPER is used to convey hw errors from platform
> to OS.

Yes or not on AMD even. 

-Andi

Re: [PATCH v4 1/4] mm/memory-failure: refactor log format in soft offline code

[Miaohe Lin]

On 2024/6/21 2:48, 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.

Thanks for your patch.

> 
> 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);

s/%#lx /%#lx: /g, i.e. ':' is missing.

>  		return 0;
>  	}
>  

Other than above possible one nit, this patch looks good to me.
Acked-by: Miaohe Lin <linmiaohe@huawei.com>
Thanks.
.

Re: [PATCH v4 2/4] mm/memory-failure: userspace controls soft-offlining pages

[Miaohe Lin]

On 2024/6/21 2:48, Jiaqi Yan wrote:
> Correctable memory errors are very common on servers with large
...
>  
>  /*
> @@ -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,
> + *         -EOPNOTSUPP if disabled by /proc/sys/vm/enable_soft_offline,

No strong opinion, but it might be better to write as "or disabled by /proc/sys/vm/enable_soft_offline".

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

Re: [PATCH v4 2/4] mm/memory-failure: userspace controls soft-offlining pages

[Jiaqi Yan]

On Sun, Jun 23, 2024 at 8:41 PM Miaohe Lin <linmiaohe@huawei.com> wrote:
>
> On 2024/6/21 2:48, Jiaqi Yan wrote:
> > Correctable memory errors are very common on servers with large
> ...
> >
> >  /*
> > @@ -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,
> > + *         -EOPNOTSUPP if disabled by /proc/sys/vm/enable_soft_offline,
>
> No strong opinion, but it might be better to write as "or disabled by /proc/sys/vm/enable_soft_offline".

Sure, will update in v5 (which is mainly about the kselftest-related changes).

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

Thanks Miaohe!

> Thanks.
> .
>