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Message-ID: <aMG6SRckMsnQH7ov@hpe.com>
Date: Wed, 10 Sep 2025 12:50:01 -0500
From: Kyle Meyer <kyle.meyer@....com>
To: Jiaqi Yan <jiaqiyan@...gle.com>
Cc: akpm@...ux-foundation.org, corbet@....net, david@...hat.com,
linmiaohe@...wei.com, shuah@...nel.org, tony.luck@...el.com,
Liam.Howlett@...cle.com, bp@...en8.de, hannes@...xchg.org,
jack@...e.cz, jane.chu@...cle.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 Wed, Sep 10, 2025 at 09:44:24AM -0700, Jiaqi Yan wrote:
> On Wed, Sep 10, 2025 at 9:16 AM Kyle Meyer <kyle.meyer@....com> 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).
>
> Would it be better to keep/inherit the previous documented behavior "1
> - Soft offline is enabled (no matter what type of the page is)"? Thus
> it will have no impact to users that are very nervous about corrected
> memory errors and willing to lose hugetlb page. Something like:
>
> enum soft_offline {
> SOFT_OFFLINE_DISABLED = 0,
> SOFT_OFFLINE_ENABLED,
> SOFT_OFFLINE_ENABLED_SKIP_HUGETLB,
> // SOFT_OFFLINE_ENABLED_SKIP_XXX...
> };
I don't have a strong opinion on the default because there's a sysctl
interface, but that seems reasonable. I'll wait for more feedback before
putting together a v2.
> > +
> > +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);
>
> Thanks for updating the test code! Looks good to me.
>
> >
> > ksft_finished();
> > }
> > --
> > 2.51.0
> >
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