On 2024/6/12 5:55, Jiaqi Yan wrote:

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.

Thanks for your update.

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.

s/mmap hugepages MAP_FAILED/fails to mmap 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:

s/doing/doing so/ ?

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 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 called enable_soft_offline under /proc/sys/vm. By default enable_soft_line is 1 to preserve existing behavior in kernel.

s/enable_soft_line/enable_soft_offline/

Signed-off-by: Jiaqi Yan jiaqiyan@google.com

mm/memory-failure.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c index d3c830e817e3..23415fe03318 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,
  

• }

}; /* @@ -2771,6 +2782,11 @@ int soft_offline_page(unsigned long pfn, int flags) bool try_again = true; struct page *page;

• if (!sysctl_enable_soft_offline) {

• pr_info("soft offline: %#lx: OS-wide disabled\n", pfn);
  

• return -EINVAL;
  

• }

IMHO, callers might reach here with page refcnt increased. So we have to take care of releasing it first? Also will it be better to return -EOPNOTSUPP or some other better errno?

Thanks. .

Hi Jiaqi,

On Wed, Jun 12, 2024 at 5:56 AM Jiaqi Yan jiaqiyan@google.com wrote:

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 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 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 called enable_soft_offline under /proc/sys/vm. By default enable_soft_line is 1 to preserve existing behavior in kernel.

s/enable_soft_line/enable_soft_offline

Signed-off-by: Jiaqi Yan jiaqiyan@google.com

mm/memory-failure.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c index d3c830e817e3..23415fe03318 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,
  

•   }
  

};

/* @@ -2771,6 +2782,11 @@ int soft_offline_page(unsigned long pfn, int flags) bool try_again = true; struct page *page;

•   if (!sysctl_enable_soft_offline) {
  

•           pr_info("soft offline: %#lx: OS-wide disabled\n", pfn);
  

•           return -EINVAL;
  

IMO, "-EPERM" might sound better ;)

Using "-EPERM" indicates that the operation is not permitted due to the OS-wide configuration.

Thanks, Lance

•   }
  

•   if (!pfn_valid(pfn)) {
            WARN_ON_ONCE(flags & MF_COUNT_INCREASED);
            return -ENXIO;
  

-- 2.45.2.505.gda0bf45e8d-goog

On 2024/6/15 0:30, Jiaqi Yan wrote:

On Fri, Jun 14, 2024 at 1:35 AM Lance Yang ioworker0@gmail.com wrote:

...

Hi Jiaqi,

On Wed, Jun 12, 2024 at 5:56 AM Jiaqi Yan jiaqiyan@google.com wrote:

...

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 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 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 called enable_soft_offline under /proc/sys/vm. By default enable_soft_line is 1 to preserve existing behavior in kernel.

s/enable_soft_line/enable_soft_offline

Will fix this typo in v3.

...

...

Signed-off-by: Jiaqi Yan jiaqiyan@google.com

mm/memory-failure.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c index d3c830e817e3..23415fe03318 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,
  

•   }
  

};

/* @@ -2771,6 +2782,11 @@ int soft_offline_page(unsigned long pfn, int flags) bool try_again = true; struct page *page;

•   if (!sysctl_enable_soft_offline) {
  

•           pr_info("soft offline: %#lx: OS-wide disabled\n", pfn);
  

•           return -EINVAL;
  

IMO, "-EPERM" might sound better ;)

Using "-EPERM" indicates that the operation is not permitted due to the OS-wide configuration.

Miaohe suggested -EOPNOTSUPP. I agree both EOPNOTSUPP and EPERM may be better than EINVAL. But I wonder how about EAGAIN? With EAGAIN plus showing "disabled by /proc/sys/vm/enable_soft_offline" in dmesg, users now should be clear that they can try again with /proc/sys/vm/enable_soft_offline=1.

IMHO, it might not be suitable to use EAGAIN. Because it means "Resource temporarily unavailable" and this can be solved by simply retry later without any further actions taken. But I might be wrong.

Thanks. .

On 2024/6/12 5:55, 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=0, mapped hugepage is soft offlined
• if enable_soft_offline=1, mapped hugepage is intact

This shoule be something like below ? if enable_soft_offline=0, mapped hugepage is intact if enable_soft_offline=1, mapped hugepage is soft offlined

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 | 258 ++++++++++++++++++ tools/testing/selftests/mm/run_vmtests.sh | 4 + 4 files changed, 264 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..d37d68a433e7 --- /dev/null +++ b/tools/testing/selftests/mm/hugetlb-soft-offline.c @@ -0,0 +1,258 @@ +// 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 == NULL)

• perror(EPREFIX "failed to set enable_soft_offline");
  

If fails to set enable_soft_offline, should we return errno here?

• else

• printf(PREFIX "enable_soft_offline => %d\n", value);
  

• 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");

Check cmdfile against NULL?

• 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(void) +{

• int fd;
• 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 softoffline_corrected_errors=1\n");
• 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(1))

• 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=*/0);
• 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 (nr_hugepages_before != nr_hugepages_after + 1) {

• printf(EPREFIX "MADV_SOFT_OFFLINE should reduced 1 hugepage\n");
  

• return TEST_FAILED;
  

• }
• return status;

+}

+static enum test_status test_disable_soft_offline(void) +{

• int fd;
• 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 softoffline_corrected_errors=0\n");
• 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(0))

• 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=*/EINVAL);
• 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 (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;

+}

test_disable_soft_offline is almost same with test_soft_offline. Shall we extract the common pattern?

Thanks. .

Thanks for your questions, David!

On Tue, Jun 11, 2024 at 5:25 PM David Rientjes rientjes@google.com wrote:

On Tue, 11 Jun 2024, Jiaqi Yan wrote:

...

@@ -267,6 +268,20 @@ 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 +=================== +Control whether to soft offline memory pages that have (excessive) correctable +memory errors. It is your call to choose between reliability (stay away from +fragile physical memory) vs performance (brought by HugeTLB or transparent +hugepages).

Could you expand upon the relevance of HugeTLB or THP in this documentation? I understand the need in some cases to soft offline memory after a number of correctable memory errors, but it's not clear how the performance implications plays into this. The paragraph below goes into a

To be accurate, I should say soft offlining transparent hugepage impacts performance, and soft offlining hugetlb hugepage impacts capacity. It may be clearer to first explain soft-offline's behaviors and implications, so that user knows what is the cost of soft-offline, then talks about the behavior of enable_soft_offline:

Correctable memory errors are very common on servers. Soft-offline is kernel's handling 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.

difference in the splitting behavior, are hugepage users the only ones that should be concerned with this?

If the cost of migrating a raw page is negligible, then yes, only hugepage users should be concerned and think about should they disable soft offline.

...

+When setting to 1, kernel attempts to soft offline the page when it thinks +needed. For in-use page, page content will be migrated to a new page. If +the oringinal hugepage is a HugeTLB hugepage, regardless of in-use or free,

s/oringinal/original/

To fix in v3.

...

+it will be dissolved into raw pages, and the capacity of the HugeTLB pool +will reduce by 1. If the original hugepage is a transparent hugepage, it +will be split into raw pages. When setting to 0, kernel won't attempt to +soft offline the page. Its default value is 1.

This behavior is the same for all architectures?

Yes, enable_soft_offline has the same behavior for all architectures, and default=1.

It may be worth mentioning that setting enable_soft_offline to 0 means: - If RAS Correctable Errors Collector is running, its request to soft offline pages will be ignored. - On ARM, the request to soft offline pages from GHES driver will be ignored. - On PARISC, the request to soft offline pages from Page Deallocation Table will be ignored.

I can add these clarifications in v3 if they are valuable.