[patch] mm, thp: add new background defrag option
From: David Rientjes
Date: Wed Jan 04 2017 - 18:42:08 EST
There is no thp defrag option that currently allows MADV_HUGEPAGE regions
to do direct compaction and reclaim while all other thp allocations simply
trigger kswapd and kcompactd in the background and fail immediately.
The "defer" setting simply triggers background reclaim and compaction for
all regions, regardless of MADV_HUGEPAGE, which makes it unusable for our
userspace where MADV_HUGEPAGE is being used to indicate the application is
willing to wait for work for thp memory to be available.
The "madvise" setting will do direct compaction and reclaim for these
MADV_HUGEPAGE regions, but does not trigger kswapd and kcompactd in the
background for anybody else.
For reasonable usage, there needs to be a mesh between the two options.
This patch introduces a fifth mode, "background", that will do direct
reclaim and compaction for MADV_HUGEPAGE regions and trigger background
reclaim and compaction for everybody else so that hugepages may be
available in the near future.
A proposal to allow direct reclaim and compaction for MADV_HUGEPAGE
regions as part of the "defer" mode, making it a very powerful setting and
avoids breaking userspace, was offered:
http://marc.info/?t=148236612700003. This additional mode is a
compromise.
This patch also cleans up the helper function for storing to "enabled"
and "defrag" since the former supports three modes while the latter
supports five and triple_flag_store() was getting unnecessarily messy.
Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
---
I don't understand Mel's suggestion of "defer-fault" as option naming.
No better idea for the naming of "background", although it is admittedly
not the best. Better suggestions are welcome.
Documentation/vm/transhuge.txt | 8 ++-
include/linux/huge_mm.h | 1 +
mm/huge_memory.c | 146 +++++++++++++++++++++--------------------
3 files changed, 82 insertions(+), 73 deletions(-)
diff --git a/Documentation/vm/transhuge.txt b/Documentation/vm/transhuge.txt
--- a/Documentation/vm/transhuge.txt
+++ b/Documentation/vm/transhuge.txt
@@ -110,6 +110,7 @@ MADV_HUGEPAGE region.
echo always >/sys/kernel/mm/transparent_hugepage/defrag
echo defer >/sys/kernel/mm/transparent_hugepage/defrag
+echo background >/sys/kernel/mm/transparent_hugepage/defrag
echo madvise >/sys/kernel/mm/transparent_hugepage/defrag
echo never >/sys/kernel/mm/transparent_hugepage/defrag
@@ -119,8 +120,13 @@ allocate a THP immediately. This may be desirable for virtual machines
that benefit heavily from THP use and are willing to delay the VM start
to utilise them.
+"background" will enter direct reclaim and compaction like "always", but
+only for regions that have used madvise(MADV_HUGEPAGE); all other regions
+will wake kswapd in the background to reclaim pages and wake kcompactd to
+compact memory so that THP is available in the near future.
+
"defer" means that an application will wake kswapd in the background
-to reclaim pages and wake kcompact to compact memory so that THP is
+to reclaim pages and wake kcompactd to compact memory so that THP is
available in the near future. It's the responsibility of khugepaged
to then install the THP pages later.
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -33,6 +33,7 @@ enum transparent_hugepage_flag {
TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG,
TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG,
+ TRANSPARENT_HUGEPAGE_DEFRAG_MADV_OR_KSWAPD_FLAG,
TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG,
TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG,
TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG,
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -142,42 +142,6 @@ static struct shrinker huge_zero_page_shrinker = {
};
#ifdef CONFIG_SYSFS
-
-static ssize_t triple_flag_store(struct kobject *kobj,
- struct kobj_attribute *attr,
- const char *buf, size_t count,
- enum transparent_hugepage_flag enabled,
- enum transparent_hugepage_flag deferred,
- enum transparent_hugepage_flag req_madv)
-{
- if (!memcmp("defer", buf,
- min(sizeof("defer")-1, count))) {
- if (enabled == deferred)
- return -EINVAL;
- clear_bit(enabled, &transparent_hugepage_flags);
- clear_bit(req_madv, &transparent_hugepage_flags);
- set_bit(deferred, &transparent_hugepage_flags);
- } else if (!memcmp("always", buf,
- min(sizeof("always")-1, count))) {
- clear_bit(deferred, &transparent_hugepage_flags);
- clear_bit(req_madv, &transparent_hugepage_flags);
- set_bit(enabled, &transparent_hugepage_flags);
- } else if (!memcmp("madvise", buf,
- min(sizeof("madvise")-1, count))) {
- clear_bit(enabled, &transparent_hugepage_flags);
- clear_bit(deferred, &transparent_hugepage_flags);
- set_bit(req_madv, &transparent_hugepage_flags);
- } else if (!memcmp("never", buf,
- min(sizeof("never")-1, count))) {
- clear_bit(enabled, &transparent_hugepage_flags);
- clear_bit(req_madv, &transparent_hugepage_flags);
- clear_bit(deferred, &transparent_hugepage_flags);
- } else
- return -EINVAL;
-
- return count;
-}
-
static ssize_t enabled_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
@@ -193,19 +157,28 @@ static ssize_t enabled_store(struct kobject *kobj,
struct kobj_attribute *attr,
const char *buf, size_t count)
{
- ssize_t ret;
+ ssize_t ret = count;
- ret = triple_flag_store(kobj, attr, buf, count,
- TRANSPARENT_HUGEPAGE_FLAG,
- TRANSPARENT_HUGEPAGE_FLAG,
- TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG);
+ if (!memcmp("always", buf,
+ min(sizeof("always")-1, count))) {
+ clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags);
+ set_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags);
+ } else if (!memcmp("madvise", buf,
+ min(sizeof("madvise")-1, count))) {
+ clear_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags);
+ set_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags);
+ } else if (!memcmp("never", buf,
+ min(sizeof("never")-1, count))) {
+ clear_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags);
+ clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags);
+ } else
+ ret = -EINVAL;
if (ret > 0) {
int err = start_stop_khugepaged();
if (err)
ret = err;
}
-
return ret;
}
static struct kobj_attribute enabled_attr =
@@ -241,32 +214,58 @@ ssize_t single_hugepage_flag_store(struct kobject *kobj,
return count;
}
-/*
- * Currently defrag only disables __GFP_NOWAIT for allocation. A blind
- * __GFP_REPEAT is too aggressive, it's never worth swapping tons of
- * memory just to allocate one more hugepage.
- */
static ssize_t defrag_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags))
- return sprintf(buf, "[always] defer madvise never\n");
+ return sprintf(buf, "[always] defer background madvise never\n");
if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags))
- return sprintf(buf, "always [defer] madvise never\n");
- else if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags))
- return sprintf(buf, "always defer [madvise] never\n");
- else
- return sprintf(buf, "always defer madvise [never]\n");
-
+ return sprintf(buf, "always [defer] background madvise never\n");
+ if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_MADV_OR_KSWAPD_FLAG, &transparent_hugepage_flags))
+ return sprintf(buf, "always defer [background] madvise never\n");
+ if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags))
+ return sprintf(buf, "always defer background [madvise] never\n");
+ return sprintf(buf, "always defer background madvise [never]\n");
}
+
static ssize_t defrag_store(struct kobject *kobj,
struct kobj_attribute *attr,
const char *buf, size_t count)
{
- return triple_flag_store(kobj, attr, buf, count,
- TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG,
- TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG,
- TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG);
+ if (!memcmp("always", buf,
+ min(sizeof("always")-1, count))) {
+ clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags);
+ clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_MADV_OR_KSWAPD_FLAG, &transparent_hugepage_flags);
+ clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags);
+ set_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags);
+ } else if (!memcmp("defer", buf,
+ min(sizeof("defer")-1, count))) {
+ clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags);
+ clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_MADV_OR_KSWAPD_FLAG, &transparent_hugepage_flags);
+ clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags);
+ set_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags);
+ } else if (!memcmp("background", buf,
+ min(sizeof("background")-1, count))) {
+ clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags);
+ clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags);
+ clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags);
+ set_bit(TRANSPARENT_HUGEPAGE_DEFRAG_MADV_OR_KSWAPD_FLAG, &transparent_hugepage_flags);
+ } else if (!memcmp("madvise", buf,
+ min(sizeof("madvise")-1, count))) {
+ clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags);
+ clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags);
+ clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_MADV_OR_KSWAPD_FLAG, &transparent_hugepage_flags);
+ set_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags);
+ } else if (!memcmp("never", buf,
+ min(sizeof("never")-1, count))) {
+ clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags);
+ clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags);
+ clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_MADV_OR_KSWAPD_FLAG, &transparent_hugepage_flags);
+ clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags);
+ } else
+ return -EINVAL;
+
+ return count;
}
static struct kobj_attribute defrag_attr =
__ATTR(defrag, 0644, defrag_show, defrag_store);
@@ -612,25 +611,28 @@ static int __do_huge_pmd_anonymous_page(struct vm_fault *vmf, struct page *page,
}
/*
- * If THP defrag is set to always then directly reclaim/compact as necessary
- * If set to defer then do only background reclaim/compact and defer to khugepaged
- * If set to madvise and the VMA is flagged then directly reclaim/compact
- * When direct reclaim/compact is allowed, don't retry except for flagged VMA's
+ * always: directly stall for all thp allocations
+ * defer: wake kswapd and fail if not immediately available
+ * background: wake kswapd and directly stall for MADV_HUGEPAGE, otherwise fail
+ * if not immediately available
+ * madvise: directly stall for MADV_HUGEPAGE, otherwise fail if not immediately
+ * available
+ * never: never stall for any thp allocation
*/
static inline gfp_t alloc_hugepage_direct_gfpmask(struct vm_area_struct *vma)
{
- bool vma_madvised = !!(vma->vm_flags & VM_HUGEPAGE);
+ const bool vma_madvised = !!(vma->vm_flags & VM_HUGEPAGE);
- if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG,
- &transparent_hugepage_flags) && vma_madvised)
- return GFP_TRANSHUGE;
- else if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG,
- &transparent_hugepage_flags))
- return GFP_TRANSHUGE_LIGHT | __GFP_KSWAPD_RECLAIM;
- else if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG,
- &transparent_hugepage_flags))
+ if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags))
return GFP_TRANSHUGE | (vma_madvised ? 0 : __GFP_NORETRY);
-
+ if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags))
+ return GFP_TRANSHUGE_LIGHT | __GFP_KSWAPD_RECLAIM;
+ if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_MADV_OR_KSWAPD_FLAG, &transparent_hugepage_flags))
+ return GFP_TRANSHUGE_LIGHT | (vma_madvised ? __GFP_DIRECT_RECLAIM :
+ __GFP_KSWAPD_RECLAIM);
+ if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags))
+ return GFP_TRANSHUGE_LIGHT | (vma_madvised ? __GFP_DIRECT_RECLAIM :
+ 0);
return GFP_TRANSHUGE_LIGHT;
}