Re: [PATCH] mm/memory-failure: Disable soft offline for HugeTLB pages by default

[jane.chu@oracle.com]

On 9/10/2025 9:15 AM, Kyle Meyer wrote:
> Soft offlining a HugeTLB page reduces the available HugeTLB page pool.
> Since HugeTLB pages are preallocated, reducing the available HugeTLB
> page pool can cause allocation failures.
> 
> /proc/sys/vm/enable_soft_offline provides a sysctl interface to
> disable/enable soft offline:
> 
> 0 - Soft offline is disabled.
> 1 - Soft offline is enabled.
> 
> The current sysctl interface does not distinguish between HugeTLB pages
> and other page types.
> 
> Disable soft offline for HugeTLB pages by default (1) and extend the
> sysctl interface to preserve existing behavior (2):
> 
> 0 - Soft offline is disabled.
> 1 - Soft offline is enabled (excluding HugeTLB pages).
> 2 - Soft offline is enabled (including HugeTLB pages).
> 
> Update documentation for the sysctl interface, reference the sysctl
> interface in the sysfs ABI documentation, and update HugeTLB soft
> offline selftests.
> 
> Reported-by: Shawn Fan <shawn.fan@intel.com>
> Suggested-by: Tony Luck <tony.luck@intel.com>
> Signed-off-by: Kyle Meyer <kyle.meyer@hpe.com>
> ---
> 
> Tony's original patch disabled soft offline for HugeTLB pages when
> a correctable memory error reported via GHES (with "error threshold
> exceeded" set) happened to be on a HugeTLB page:
> 
> https://lore.kernel.org/all/20250904155720.22149-1-tony.luck@intel.com
> 
> This patch disables soft offline for HugeTLB pages by default
> (not just from GHES).
> 
> ---
>   .../ABI/testing/sysfs-memory-page-offline     |  6 ++++
>   Documentation/admin-guide/sysctl/vm.rst       | 18 ++++++++---
>   mm/memory-failure.c                           | 21 ++++++++++--
>   .../selftests/mm/hugetlb-soft-offline.c       | 32 +++++++++++++------
>   4 files changed, 60 insertions(+), 17 deletions(-)
> 
> diff --git a/Documentation/ABI/testing/sysfs-memory-page-offline b/Documentation/ABI/testing/sysfs-memory-page-offline
> index 00f4e35f916f..befb89ae39ec 100644
> --- a/Documentation/ABI/testing/sysfs-memory-page-offline
> +++ b/Documentation/ABI/testing/sysfs-memory-page-offline
> @@ -20,6 +20,12 @@ Description:
>   		number, or a error when the offlining failed.  Reading
>   		the file is not allowed.
>   
> +		Soft-offline can be disabled/enabled via sysctl:
> +		/proc/sys/vm/enable_soft_offline
> +
> +		For details, see:
> +		Documentation/admin-guide/sysctl/vm.rst
> +
>   What:		/sys/devices/system/memory/hard_offline_page
>   Date:		Sep 2009
>   KernelVersion:	2.6.33
> diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst
> index 4d71211fdad8..ae56372bd604 100644
> --- a/Documentation/admin-guide/sysctl/vm.rst
> +++ b/Documentation/admin-guide/sysctl/vm.rst
> @@ -309,19 +309,29 @@ 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 set to 1, kernel attempts to soft offline the pages
> -whenever it thinks needed.  When set to 0, kernel returns EOPNOTSUPP to
> -the request to soft offline the pages.  Its default value is 1.
> +memory pages:
> +
> +- 0: Soft offline is disabled.
> +- 1: Soft offline is enabled (excluding HugeTLB pages).
> +- 2: Soft offline is enabled (including HugeTLB pages).
> +
> +The default is 1.
> +
> +If soft offline is disabled for the requested page type, EOPNOTSUPP is returned.
>   
>   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 from sysfs (soft_offline_page).
> +
>   - Request to soft offline pages from RAS Correctable Errors Collector.
>   
> -- On ARM, the request to soft offline pages from GHES driver.
> +- On ARM and X86, the request to soft offline pages from GHES driver.
>   
>   - On PARISC, the request to soft offline pages from Page Deallocation Table.
>   
> +Note: Soft offlining a HugeTLB page reduces the HugeTLB page pool.
> +
>   extfrag_threshold
>   =================
>   
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index fc30ca4804bf..cb59a99b48c5 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -64,11 +64,18 @@
>   #include "internal.h"
>   #include "ras/ras_event.h"
>   
> +enum soft_offline {
> +	SOFT_OFFLINE_DISABLED = 0,
> +	SOFT_OFFLINE_ENABLED_SKIP_HUGETLB,
> +	SOFT_OFFLINE_ENABLED
> +};
> +
>   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;
> +static int sysctl_enable_soft_offline __read_mostly =
> +	SOFT_OFFLINE_ENABLED_SKIP_HUGETLB;
>   
>   atomic_long_t num_poisoned_pages __read_mostly = ATOMIC_LONG_INIT(0);
>   
> @@ -150,7 +157,7 @@ static const struct ctl_table memory_failure_table[] = {
>   		.mode		= 0644,
>   		.proc_handler	= proc_dointvec_minmax,
>   		.extra1		= SYSCTL_ZERO,
> -		.extra2		= SYSCTL_ONE,
> +		.extra2		= SYSCTL_TWO,
>   	}
>   };
>   
> @@ -2799,12 +2806,20 @@ int soft_offline_page(unsigned long pfn, int flags)
>   		return -EIO;
>   	}
>   
> -	if (!sysctl_enable_soft_offline) {
> +	if (sysctl_enable_soft_offline == SOFT_OFFLINE_DISABLED) {
>   		pr_info_once("disabled by /proc/sys/vm/enable_soft_offline\n");
>   		put_ref_page(pfn, flags);
>   		return -EOPNOTSUPP;
>   	}
>   
> +	if (sysctl_enable_soft_offline == SOFT_OFFLINE_ENABLED_SKIP_HUGETLB) {
> +		if (folio_test_hugetlb(pfn_folio(pfn))) {
> +			pr_info_once("disabled for HugeTLB pages by /proc/sys/vm/enable_soft_offline\n");
> +			put_ref_page(pfn, flags);
> +			return -EOPNOTSUPP;
> +		}
> +	}
> +
>   	mutex_lock(&mf_mutex);
>   
>   	if (PageHWPoison(page)) {
> diff --git a/tools/testing/selftests/mm/hugetlb-soft-offline.c b/tools/testing/selftests/mm/hugetlb-soft-offline.c
> index f086f0e04756..7e2873cd0a6d 100644
> --- a/tools/testing/selftests/mm/hugetlb-soft-offline.c
> +++ b/tools/testing/selftests/mm/hugetlb-soft-offline.c
> @@ -1,10 +1,15 @@
>   // 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 EOPNOTSUPP.
> - * - if enable_soft_offline = 1, a hugepage should be dissolved and
> - *   nr_hugepages/free_hugepages should be reduced by 1.
> + *
> + * - if enable_soft_offline = 0 (SOFT_OFFLINE_DISABLED), HugeTLB pages
> + *   should stay intact and soft offlining failed with EOPNOTSUPP.
> + *
> + * - if enable_soft_offline = 1 (SOFT_OFFLINE_ENABLED_SKIP_HUGETLB), HugeTLB pages
> + *   should stay intact and soft offlining failed with EOPNOTSUPP.
> + *
> + * - if enable_soft_offline = 2 (SOFT_OFFLINE_ENABLED), a HugeTLB page 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:
> @@ -32,6 +37,12 @@
>   
>   #define EPREFIX " !!! "
>   
> +enum soft_offline {
> +	SOFT_OFFLINE_DISABLED = 0,
> +	SOFT_OFFLINE_ENABLED_SKIP_HUGETLB,
> +	SOFT_OFFLINE_ENABLED
> +};
> +
>   static int do_soft_offline(int fd, size_t len, int expect_errno)
>   {
>   	char *filemap = NULL;
> @@ -83,7 +94,7 @@ static int set_enable_soft_offline(int value)
>   	char cmd[256] = {0};
>   	FILE *cmdfile = NULL;
>   
> -	if (value != 0 && value != 1)
> +	if (value < SOFT_OFFLINE_DISABLED || value > SOFT_OFFLINE_ENABLED)
>   		return -EINVAL;
>   
>   	sprintf(cmd, "echo %d > /proc/sys/vm/enable_soft_offline", value);
> @@ -155,7 +166,7 @@ static int create_hugetlbfs_file(struct statfs *file_stat)
>   static void test_soft_offline_common(int enable_soft_offline)
>   {
>   	int fd;
> -	int expect_errno = enable_soft_offline ? 0 : EOPNOTSUPP;
> +	int expect_errno = (enable_soft_offline == SOFT_OFFLINE_ENABLED) ? 0 : EOPNOTSUPP;
>   	struct statfs file_stat;
>   	unsigned long hugepagesize_kb = 0;
>   	unsigned long nr_hugepages_before = 0;
> @@ -198,7 +209,7 @@ static void test_soft_offline_common(int enable_soft_offline)
>   	// No need for the hugetlbfs file from now on.
>   	close(fd);
>   
> -	if (enable_soft_offline) {
> +	if (enable_soft_offline == SOFT_OFFLINE_ENABLED) {
>   		if (nr_hugepages_before != nr_hugepages_after + 1) {
>   			ksft_test_result_fail("MADV_SOFT_OFFLINE should reduced 1 hugepage\n");
>   			return;
> @@ -219,10 +230,11 @@ static void test_soft_offline_common(int enable_soft_offline)
>   int main(int argc, char **argv)
>   {
>   	ksft_print_header();
> -	ksft_set_plan(2);
> +	ksft_set_plan(3);
>   
> -	test_soft_offline_common(1);
> -	test_soft_offline_common(0);
> +	test_soft_offline_common(SOFT_OFFLINE_ENABLED);
> +	test_soft_offline_common(SOFT_OFFLINE_ENABLED_SKIP_HUGETLB);
> +	test_soft_offline_common(SOFT_OFFLINE_DISABLED);
>   
>   	ksft_finished();
>   }

Looks good to me.
Reviewed-by: Jane Chu <jane.chu@oracle.com>

Thanks!
-jane