[PATCH v4 3/6] mm: shmem: add multi-size THP sysfs interface for anonymous shmem

Baolin Wang
2024-06-04T10:18:16Z

To support the use of mTHP with anonymous shmem, add a new sysfs interface
'shmem_enabled' in the '/sys/kernel/mm/transparent_hugepage/hugepages-kB/'
directory for each mTHP to control whether shmem is enabled for that mTHP,
with a value similar to the top level 'shmem_enabled', which can be set to:
"always", "inherit (to inherit the top level setting)", "within_size", "advise",
"never". An 'inherit' option is added to ensure compatibility with these
global settings, and the options 'force' and 'deny' are dropped, which are
rather testing artifacts from the old ages.

By default, PMD-sized hugepages have enabled="inherit" and all other hugepage
sizes have enabled="never" for '/sys/kernel/mm/transparent_hugepage/hugepages-xxkB/shmem_enabled'.

In addition, if top level value is 'force', then only PMD-sized hugepages
have enabled="inherit", otherwise configuration will be failed and vice versa.
That means now we will avoid using non-PMD sized THP to override the global
huge allocation.

Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
---
Documentation/admin-guide/mm/transhuge.rst | 23 ++++++
include/linux/huge_mm.h | 10 +++
mm/huge_memory.c | 11 +--
mm/shmem.c | 96 ++++++++++++++++++++++
4 files changed, 132 insertions(+), 8 deletions(-)

diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst
index d414d3f5592a..b76d15e408b3 100644
--- a/Documentation/admin-guide/mm/transhuge.rst
+++ b/Documentation/admin-guide/mm/transhuge.rst
@@ -332,6 +332,29 @@ deny
force
Force the huge option on for all - very useful for testing;

+Shmem can also use "multi-size THP" (mTHP) by adding a new sysfs knob to control
+mTHP allocation: '/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/shmem_enabled',
+and its value for each mTHP is essentially consistent with the global setting.
+An 'inherit' option is added to ensure compatibility with these global settings.
+Conversely, the options 'force' and 'deny' are dropped, which are rather testing
+artifacts from the old ages.
+always
+ Attempt to allocate <size> huge pages every time we need a new page;
+
+inherit
+ Inherit the top-level "shmem_enabled" value. By default, PMD-sized hugepages
+ have enabled="inherit" and all other hugepage sizes have enabled="never";
+
+never
+ Do not allocate <size> huge pages;
+
+within_size
+ Only allocate <size> huge page if it will be fully within i_size.
+ Also respect fadvise()/madvise() hints;
+
+advise
+ Only allocate <size> huge pages if requested with fadvise()/madvise();
+
Need of application restart
===========================

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 020e2344eb86..fac21548c5de 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -6,6 +6,7 @@
#include <linux/mm_types.h>

#include <linux/fs.h> /* only for vma_is_dax() */
+#include <linux/kobject.h>

vm_fault_t do_huge_pmd_anonymous_page(struct vm_fault *vmf);
int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
@@ -63,6 +64,7 @@ ssize_t single_hugepage_flag_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf,
enum transparent_hugepage_flag flag);
extern struct kobj_attribute shmem_enabled_attr;
+extern struct kobj_attribute thpsize_shmem_enabled_attr;

/*
* Mask of all large folio orders supported for anonymous THP; all orders up to
@@ -265,6 +267,14 @@ unsigned long thp_vma_allowable_orders(struct vm_area_struct *vma,
return __thp_vma_allowable_orders(vma, vm_flags, tva_flags, orders);
}

+struct thpsize {
+ struct kobject kobj;
+ struct list_head node;
+ int order;
+};
+
+#define to_thpsize(kobj) container_of(kobj, struct thpsize, kobj)
+
enum mthp_stat_item {
MTHP_STAT_ANON_FAULT_ALLOC,
MTHP_STAT_ANON_FAULT_FALLBACK,
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 8e49f402d7c7..1360a1903b66 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -449,14 +449,6 @@ static void thpsize_release(struct kobject *kobj);
static DEFINE_SPINLOCK(huge_anon_orders_lock);
static LIST_HEAD(thpsize_list);

-struct thpsize {
- struct kobject kobj;
- struct list_head node;
- int order;
-};
-
-#define to_thpsize(kobj) container_of(kobj, struct thpsize, kobj)
-
static ssize_t thpsize_enabled_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
@@ -517,6 +509,9 @@ static struct kobj_attribute thpsize_enabled_attr =

static struct attribute *thpsize_attrs[] = {
&thpsize_enabled_attr.attr,
+#ifdef CONFIG_SHMEM
+ &thpsize_shmem_enabled_attr.attr,
+#endif
NULL,
};

diff --git a/mm/shmem.c b/mm/shmem.c
index ae358efc397a..643ff7516b4d 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -131,6 +131,14 @@ struct shmem_options {
#define SHMEM_SEEN_QUOTA 32
};

+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+static unsigned long huge_anon_shmem_orders_always __read_mostly;
+static unsigned long huge_anon_shmem_orders_madvise __read_mostly;
+static unsigned long huge_anon_shmem_orders_inherit __read_mostly;
+static unsigned long huge_anon_shmem_orders_within_size __read_mostly;
+static DEFINE_SPINLOCK(huge_anon_shmem_orders_lock);
+#endif
+
#ifdef CONFIG_TMPFS
static unsigned long shmem_default_max_blocks(void)
{
@@ -4672,6 +4680,12 @@ void __init shmem_init(void)
SHMEM_SB(shm_mnt->mnt_sb)->huge = shmem_huge;
else
shmem_huge = SHMEM_HUGE_NEVER; /* just in case it was patched */
+
+ /*
+ * Default to setting PMD-sized THP to inherit the global setting and
+ * disable all other multi-size THPs, when anonymous shmem uses mTHP.
+ */
+ huge_anon_shmem_orders_inherit = BIT(HPAGE_PMD_ORDER);
#endif
return;

@@ -4731,6 +4745,11 @@ static ssize_t shmem_enabled_store(struct kobject *kobj,
huge != SHMEM_HUGE_NEVER && huge != SHMEM_HUGE_DENY)
return -EINVAL;

+ /* Do not override huge allocation policy with non-PMD sized mTHP */
+ if (huge == SHMEM_HUGE_FORCE &&
+ huge_anon_shmem_orders_inherit != BIT(HPAGE_PMD_ORDER))
+ return -EINVAL;
+
shmem_huge = huge;
if (shmem_huge > SHMEM_HUGE_DENY)
SHMEM_SB(shm_mnt->mnt_sb)->huge = shmem_huge;
@@ -4738,6 +4757,83 @@ static ssize_t shmem_enabled_store(struct kobject *kobj,
}

struct kobj_attribute shmem_enabled_attr = __ATTR_RW(shmem_enabled);
+
+static ssize_t thpsize_shmem_enabled_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ int order = to_thpsize(kobj)->order;
+ const char *output;
+
+ if (test_bit(order, &huge_anon_shmem_orders_always))
+ output = "[always] inherit within_size advise never";
+ else if (test_bit(order, &huge_anon_shmem_orders_inherit))
+ output = "always [inherit] within_size advise never";
+ else if (test_bit(order, &huge_anon_shmem_orders_within_size))
+ output = "always inherit [within_size] advise never";
+ else if (test_bit(order, &huge_anon_shmem_orders_madvise))
+ output = "always inherit within_size [advise] never";
+ else
+ output = "always inherit within_size advise [never]";
+
+ return sysfs_emit(buf, "%s\n", output);
+}
+
+static ssize_t thpsize_shmem_enabled_store(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ const char *buf, size_t count)
+{
+ int order = to_thpsize(kobj)->order;
+ ssize_t ret = count;
+
+ if (sysfs_streq(buf, "always")) {
+ spin_lock(&huge_anon_shmem_orders_lock);
+ clear_bit(order, &huge_anon_shmem_orders_inherit);
+ clear_bit(order, &huge_anon_shmem_orders_madvise);
+ clear_bit(order, &huge_anon_shmem_orders_within_size);
+ set_bit(order, &huge_anon_shmem_orders_always);
+ spin_unlock(&huge_anon_shmem_orders_lock);
+ } else if (sysfs_streq(buf, "inherit")) {
+ /* Do not override huge allocation policy with non-PMD sized mTHP */
+ if (shmem_huge == SHMEM_HUGE_FORCE &&
+ order != HPAGE_PMD_ORDER)
+ return -EINVAL;
+
+ spin_lock(&huge_anon_shmem_orders_lock);
+ clear_bit(order, &huge_anon_shmem_orders_always);
+ clear_bit(order, &huge_anon_shmem_orders_madvise);
+ clear_bit(order, &huge_anon_shmem_orders_within_size);
+ set_bit(order, &huge_anon_shmem_orders_inherit);
+ spin_unlock(&huge_anon_shmem_orders_lock);
+ } else if (sysfs_streq(buf, "within_size")) {
+ spin_lock(&huge_anon_shmem_orders_lock);
+ clear_bit(order, &huge_anon_shmem_orders_always);
+ clear_bit(order, &huge_anon_shmem_orders_inherit);
+ clear_bit(order, &huge_anon_shmem_orders_madvise);
+ set_bit(order, &huge_anon_shmem_orders_within_size);
+ spin_unlock(&huge_anon_shmem_orders_lock);
+ } else if (sysfs_streq(buf, "madvise")) {
+ spin_lock(&huge_anon_shmem_orders_lock);
+ clear_bit(order, &huge_anon_shmem_orders_always);
+ clear_bit(order, &huge_anon_shmem_orders_inherit);
+ clear_bit(order, &huge_anon_shmem_orders_within_size);
+ set_bit(order, &huge_anon_shmem_orders_madvise);
+ spin_unlock(&huge_anon_shmem_orders_lock);
+ } else if (sysfs_streq(buf, "never")) {
+ spin_lock(&huge_anon_shmem_orders_lock);
+ clear_bit(order, &huge_anon_shmem_orders_always);
+ clear_bit(order, &huge_anon_shmem_orders_inherit);
+ clear_bit(order, &huge_anon_shmem_orders_within_size);
+ clear_bit(order, &huge_anon_shmem_orders_madvise);
+ spin_unlock(&huge_anon_shmem_orders_lock);
+ } else {
+ ret = -EINVAL;
+ }
+
+ return ret;
+}
+
+struct kobj_attribute thpsize_shmem_enabled_attr =
+ __ATTR(shmem_enabled, 0644, thpsize_shmem_enabled_show, thpsize_shmem_enabled_store);
#endif /* CONFIG_TRANSPARENT_HUGEPAGE && CONFIG_SYSFS */

#else /* !CONFIG_SHMEM */
--
2.39.3