[PATCH -V6 11/21] swap: Add sysfs interface to configure THP swapin

Huang Ying
2018-10-10T07:28:43Z

Swapin a THP as a whole isn't desirable in some situations. For
example, for completely random access pattern, swapin a THP in one
piece will inflate the reading greatly. So a sysfs interface:
/sys/kernel/mm/transparent_hugepage/swapin_enabled is added to
configure it. Three options as follow are provided,

- always: THP swapin will be enabled always

- madvise: THP swapin will be enabled only for VMA with VM_HUGEPAGE
flag set.

- never: THP swapin will be disabled always

The default configuration is: madvise.

During page fault, if a PMD swap mapping is found and THP swapin is
disabled, the huge swap cluster and the PMD swap mapping will be split
and fallback to normal page swapin.

Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Shaohua Li <shli@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Zi Yan <zi.yan@cs.rutgers.edu>
Cc: Daniel Jordan <daniel.m.jordan@oracle.com>
---
Documentation/admin-guide/mm/transhuge.rst | 21 +++++++
include/linux/huge_mm.h | 31 ++++++++++
mm/huge_memory.c | 94 ++++++++++++++++++++++++------
3 files changed, 127 insertions(+), 19 deletions(-)

diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst
index 85e33f785fd7..23aefb17101c 100644
--- a/Documentation/admin-guide/mm/transhuge.rst
+++ b/Documentation/admin-guide/mm/transhuge.rst
@@ -160,6 +160,27 @@ Some userspace (such as a test program, or an optimized memory allocation

cat /sys/kernel/mm/transparent_hugepage/hpage_pmd_size

+Transparent hugepage may be swapout and swapin in one piece without
+splitting. This will improve the utility of transparent hugepage but
+may inflate the read/write too. So whether to enable swapin
+transparent hugepage in one piece can be configured as follow.
+
+ echo always >/sys/kernel/mm/transparent_hugepage/swapin_enabled
+ echo madvise >/sys/kernel/mm/transparent_hugepage/swapin_enabled
+ echo never >/sys/kernel/mm/transparent_hugepage/swapin_enabled
+
+always
+ Attempt to allocate a transparent huge page and read it from
+ swap space in one piece every time.
+
+never
+ Always split the swap space and PMD swap mapping and swapin
+ the fault normal page during swapin.
+
+madvise
+ Only swapin the transparent huge page in one piece for
+ MADV_HUGEPAGE madvise regions.
+
khugepaged will be automatically started when
transparent_hugepage/enabled is set to "always" or "madvise, and it'll
be automatically shutdown if it's set to "never".
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index d88579cb059a..a13cd19b6047 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -63,6 +63,8 @@ enum transparent_hugepage_flag {
#ifdef CONFIG_DEBUG_VM
TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG,
#endif
+ TRANSPARENT_HUGEPAGE_SWAPIN_FLAG,
+ TRANSPARENT_HUGEPAGE_SWAPIN_REQ_MADV_FLAG,
};

struct kobject;
@@ -375,11 +377,40 @@ static inline gfp_t alloc_hugepage_direct_gfpmask(struct vm_area_struct *vma,

#ifdef CONFIG_THP_SWAP
extern int do_huge_pmd_swap_page(struct vm_fault *vmf, pmd_t orig_pmd);
+
+static inline bool transparent_hugepage_swapin_enabled(
+ struct vm_area_struct *vma)
+{
+ if (vma->vm_flags & VM_NOHUGEPAGE)
+ return false;
+
+ if (is_vma_temporary_stack(vma))
+ return false;
+
+ if (test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
+ return false;
+
+ if (transparent_hugepage_flags &
+ (1 << TRANSPARENT_HUGEPAGE_SWAPIN_FLAG))
+ return true;
+
+ if (transparent_hugepage_flags &
+ (1 << TRANSPARENT_HUGEPAGE_SWAPIN_REQ_MADV_FLAG))
+ return !!(vma->vm_flags & VM_HUGEPAGE);
+
+ return false;
+}
#else /* CONFIG_THP_SWAP */
static inline int do_huge_pmd_swap_page(struct vm_fault *vmf, pmd_t orig_pmd)
{
return 0;
}
+
+static inline bool transparent_hugepage_swapin_enabled(
+ struct vm_area_struct *vma)
+{
+ return false;
+}
#endif /* CONFIG_THP_SWAP */

#endif /* _LINUX_HUGE_MM_H */
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 8efcc84fb4b0..0ccb1b78d661 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -57,7 +57,8 @@ unsigned long transparent_hugepage_flags __read_mostly =
#endif
(1<<TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG)|
(1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG)|
- (1<<TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
+ (1<<TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG)|
+ (1<<TRANSPARENT_HUGEPAGE_SWAPIN_REQ_MADV_FLAG);

static struct shrinker deferred_split_shrinker;

@@ -316,6 +317,53 @@ static struct kobj_attribute debug_cow_attr =
__ATTR(debug_cow, 0644, debug_cow_show, debug_cow_store);
#endif /* CONFIG_DEBUG_VM */

+#ifdef CONFIG_THP_SWAP
+static ssize_t swapin_enabled_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ if (test_bit(TRANSPARENT_HUGEPAGE_SWAPIN_FLAG,
+ &transparent_hugepage_flags))
+ return sprintf(buf, "[always] madvise never\n");
+ else if (test_bit(TRANSPARENT_HUGEPAGE_SWAPIN_REQ_MADV_FLAG,
+ &transparent_hugepage_flags))
+ return sprintf(buf, "always [madvise] never\n");
+ else
+ return sprintf(buf, "always madvise [never]\n");
+}
+
+static ssize_t swapin_enabled_store(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ const char *buf, size_t count)
+{
+ ssize_t ret = count;
+
+ if (!memcmp("always", buf,
+ min(sizeof("always")-1, count))) {
+ clear_bit(TRANSPARENT_HUGEPAGE_SWAPIN_REQ_MADV_FLAG,
+ &transparent_hugepage_flags);
+ set_bit(TRANSPARENT_HUGEPAGE_SWAPIN_FLAG,
+ &transparent_hugepage_flags);
+ } else if (!memcmp("madvise", buf,
+ min(sizeof("madvise")-1, count))) {
+ clear_bit(TRANSPARENT_HUGEPAGE_SWAPIN_FLAG,
+ &transparent_hugepage_flags);
+ set_bit(TRANSPARENT_HUGEPAGE_SWAPIN_REQ_MADV_FLAG,
+ &transparent_hugepage_flags);
+ } else if (!memcmp("never", buf,
+ min(sizeof("never")-1, count))) {
+ clear_bit(TRANSPARENT_HUGEPAGE_SWAPIN_FLAG,
+ &transparent_hugepage_flags);
+ clear_bit(TRANSPARENT_HUGEPAGE_SWAPIN_REQ_MADV_FLAG,
+ &transparent_hugepage_flags);
+ } else
+ ret = -EINVAL;
+
+ return ret;
+}
+static struct kobj_attribute swapin_enabled_attr =
+ __ATTR(swapin_enabled, 0644, swapin_enabled_show, swapin_enabled_store);
+#endif /* CONFIG_THP_SWAP */
+
static struct attribute *hugepage_attr[] = {
&enabled_attr.attr,
&defrag_attr.attr,
@@ -326,6 +374,9 @@ static struct attribute *hugepage_attr[] = {
#endif
#ifdef CONFIG_DEBUG_VM
&debug_cow_attr.attr,
+#endif
+#ifdef CONFIG_THP_SWAP
+ &swapin_enabled_attr.attr,
#endif
NULL,
};
@@ -1695,6 +1746,9 @@ int do_huge_pmd_swap_page(struct vm_fault *vmf, pmd_t orig_pmd)
retry:
page = lookup_swap_cache(entry, NULL, vmf->address);
if (!page) {
+ if (!transparent_hugepage_swapin_enabled(vma))
+ goto split;
+
page = read_swap_cache_async(entry, GFP_HIGHUSER_MOVABLE, vma,
haddr, false);
if (!page) {
@@ -1702,24 +1756,8 @@ int do_huge_pmd_swap_page(struct vm_fault *vmf, pmd_t orig_pmd)
* Back out if somebody else faulted in this pmd
* while we released the pmd lock.
*/
- if (likely(pmd_same(*vmf->pmd, orig_pmd))) {
- /*
- * Failed to allocate huge page, split huge swap
- * cluster, and fallback to swapin normal page
- */
- ret = split_swap_cluster(entry, 0);
- /* Somebody else swapin the swap entry, retry */
- if (ret == -EEXIST) {
- ret = 0;
- goto retry;
- /* swapoff occurs under us */
- } else if (ret == -EINVAL)
- ret = 0;
- else {
- count_vm_event(THP_SWPIN_FALLBACK);
- goto fallback;
- }
- }
+ if (likely(pmd_same(*vmf->pmd, orig_pmd)))
+ goto split;
delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
goto out;
}
@@ -1832,6 +1870,24 @@ int do_huge_pmd_swap_page(struct vm_fault *vmf, pmd_t orig_pmd)
if (page)
put_page(page);
return ret;
+split:
+ /*
+ * Failed to allocate huge page, split huge swap cluster, and
+ * fallback to swapin normal page
+ */
+ ret = split_swap_cluster(entry, 0);
+ /* Somebody else swapin the swap entry, retry */
+ if (ret == -EEXIST) {
+ ret = 0;
+ goto retry;
+ }
+ /* swapoff occurs under us */
+ if (ret == -EINVAL) {
+ delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
+ return 0;
+ }
+ count_vm_event(THP_SWPIN_FALLBACK);
+ goto fallback;
}
#endif

--
2.16.4