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Message-ID: <c30e8d18-57ec-4bd2-a5f1-29f8d684abf2@oracle.com>
Date: Wed, 10 Sep 2025 11:05:43 -0700
From: jane.chu@...cle.com
To: Kyle Meyer <kyle.meyer@....com>, akpm@...ux-foundation.org, corbet@....net,
david@...hat.com, linmiaohe@...wei.com, shuah@...nel.org,
tony.luck@...el.com
Cc: Liam.Howlett@...cle.com, bp@...en8.de, hannes@...xchg.org, jack@...e.cz,
jiaqiyan@...gle.com, joel.granados@...nel.org, laoar.shao@...il.com,
lorenzo.stoakes@...cle.com, mclapinski@...gle.com, mhocko@...e.com,
nao.horiguchi@...il.com, osalvador@...e.de, rafael.j.wysocki@...el.com,
rppt@...nel.org, russ.anderson@....com, shawn.fan@...el.com,
surenb@...gle.com, vbabka@...e.cz, linux-acpi@...r.kernel.org,
linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-kselftest@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm/memory-failure: Disable soft offline for HugeTLB pages
by default
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@...el.com>
> Suggested-by: Tony Luck <tony.luck@...el.com>
> Signed-off-by: Kyle Meyer <kyle.meyer@....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@...cle.com>
Thanks!
-jane
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