[PATCH] mm: hugetlb controller for cgroups v2

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In the effort of supporting cgroups v2 into Kubernetes, I stumped on
the lack of the hugetlb controller.

When the controller is enabled, it exposes three new files for each
hugetlb size on non-root cgroups:

- hugetlb.<hugepagesize>.current
- hugetlb.<hugepagesize>.max
- hugetlb.<hugepagesize>.stat

The differences with the legacy hierarchy are in the file names and
using the value "max" instead of "-1" to disable a limit.

The file .limit_in_bytes is renamed to .max.

The file .usage_in_bytes is renamed to .usage.

.failcnt and .max_usage_in_bytes are not provided as single files
anymore, but their value can be read through the new flat-keyed file
.stat, respectively through the max_usage and failcnt keys.

Signed-off-by: Giuseppe Scrivano <gscrivan@xxxxxxxxxx>
---
 Documentation/admin-guide/cgroup-v2.rst |  28 +++++
 include/linux/hugetlb.h                 |   3 +-
 mm/hugetlb_cgroup.c                     | 142 ++++++++++++++++++++++--
 3 files changed, 162 insertions(+), 11 deletions(-)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 5361ebec3361..662cb39abbf5 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -61,6 +61,8 @@ v1 is available under Documentation/admin-guide/cgroup-v1/.
      5-6. Device
      5-7. RDMA
        5-7-1. RDMA Interface Files
+     5-8. HugeTLB
+       5.8-1. HugeTLB Interface Files
      5-8. Misc
        5-8-1. perf_event
      5-N. Non-normative information
@@ -2050,6 +2052,32 @@ RDMA Interface Files
 	  mlx4_0 hca_handle=1 hca_object=20
 	  ocrdma1 hca_handle=1 hca_object=23
 
+HugeTLB
+-------
+
+The HugeTLB controller allows to limit the HugeTLB usage per control group and
+enforces the controller limit during page fault.
+
+HugeTLB Interface Files
+~~~~~~~~~~~~~~~~~~~~~~~
+
+  hugetlb.<hugepagesize>.current
+	Show current usage for "hugepagesize" hugetlb.  The default
+	value is "max".  It exists for all the cgroup except root.
+
+
+  hugetlb.<hugepagesize>.max
+	Set/show the hard limit of "hugepagesize" hugetlb usage.
+	The default value is "max".  It exists for all the cgroup except root.
+
+  hugetlb.<hugepagesize>.stat
+	A read-only flat-keyed file which exists on non-root cgroups.
+
+	  max_usage
+		Maximum HugeTLB usage recorded
+
+	  failcnt
+		The number of allocation failure due to HugeTLB limit
 
 Misc
 ----
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 53fc34f930d0..1c2bacbca044 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -340,7 +340,8 @@ struct hstate {
 	unsigned int surplus_huge_pages_node[MAX_NUMNODES];
 #ifdef CONFIG_CGROUP_HUGETLB
 	/* cgroup control files */
-	struct cftype cgroup_files[5];
+	struct cftype cgroup_files_dfl[5];
+	struct cftype cgroup_files_legacy[5];
 #endif
 	char name[HSTATE_NAME_LEN];
 };
diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c
index 2ac38bdc18a1..d4dbf5203324 100644
--- a/mm/hugetlb_cgroup.c
+++ b/mm/hugetlb_cgroup.c
@@ -283,10 +283,55 @@ static u64 hugetlb_cgroup_read_u64(struct cgroup_subsys_state *css,
 	}
 }
 
+static int hugetlb_cgroup_read_u64_max(struct seq_file *seq, void *v)
+{
+	int idx;
+	u64 val;
+	bool write_raw = false;
+	struct cftype *cft = seq_cft(seq);
+	unsigned long limit;
+	struct page_counter *counter;
+	struct hugetlb_cgroup *h_cg = hugetlb_cgroup_from_css(seq_css(seq));
+
+	idx = MEMFILE_IDX(cft->private);
+	counter = &h_cg->hugepage[idx];
+
+	switch (MEMFILE_ATTR(cft->private)) {
+	case RES_USAGE:
+		val = (u64)page_counter_read(counter);
+		break;
+	case RES_LIMIT:
+		val = (u64)counter->max;
+		break;
+	case RES_MAX_USAGE:
+		val = (u64)counter->watermark;
+		break;
+	case RES_FAILCNT:
+		val = counter->failcnt;
+		write_raw = true;
+		break;
+	default:
+		BUG();
+	}
+
+	limit = round_down(PAGE_COUNTER_MAX,
+			   1 << huge_page_order(&hstates[idx]));
+
+	if (val == limit && !write_raw)
+		seq_puts(seq, "max\n");
+	else if (write_raw)
+		seq_printf(seq, "%llu\n", val);
+	else
+		seq_printf(seq, "%llu\n", val * PAGE_SIZE);
+
+	return 0;
+}
+
 static DEFINE_MUTEX(hugetlb_limit_mutex);
 
 static ssize_t hugetlb_cgroup_write(struct kernfs_open_file *of,
-				    char *buf, size_t nbytes, loff_t off)
+				    char *buf, size_t nbytes, loff_t off,
+				    const char *max)
 {
 	int ret, idx;
 	unsigned long nr_pages;
@@ -296,7 +341,7 @@ static ssize_t hugetlb_cgroup_write(struct kernfs_open_file *of,
 		return -EINVAL;
 
 	buf = strstrip(buf);
-	ret = page_counter_memparse(buf, "-1", &nr_pages);
+	ret = page_counter_memparse(buf, max, &nr_pages);
 	if (ret)
 		return ret;
 
@@ -316,6 +361,18 @@ static ssize_t hugetlb_cgroup_write(struct kernfs_open_file *of,
 	return ret ?: nbytes;
 }
 
+static ssize_t hugetlb_cgroup_write_legacy(struct kernfs_open_file *of,
+					   char *buf, size_t nbytes, loff_t off)
+{
+	return hugetlb_cgroup_write(of, buf, nbytes, off, "-1");
+}
+
+static ssize_t hugetlb_cgroup_write_dfl(struct kernfs_open_file *of,
+					char *buf, size_t nbytes, loff_t off)
+{
+	return hugetlb_cgroup_write(of, buf, nbytes, off, "max");
+}
+
 static ssize_t hugetlb_cgroup_reset(struct kernfs_open_file *of,
 				    char *buf, size_t nbytes, loff_t off)
 {
@@ -350,7 +407,60 @@ static char *mem_fmt(char *buf, int size, unsigned long hsize)
 	return buf;
 }
 
-static void __init __hugetlb_cgroup_file_init(int idx)
+static int hugetlb_stat_show(struct seq_file *seq, void *v)
+{
+	struct page_counter *counter;
+	struct cftype *cft = seq_cft(seq);
+	struct hugetlb_cgroup *h_cg = hugetlb_cgroup_from_css(seq_css(seq));
+
+	counter = &h_cg->hugepage[MEMFILE_IDX(cft->private)];
+
+	seq_printf(seq, "max_usage %llu\n",
+		   (u64)counter->watermark * PAGE_SIZE);
+	seq_printf(seq, "fail_cnt %lu\n", counter->failcnt);
+
+	return 0;
+}
+
+static void __init __hugetlb_cgroup_file_dfl_init(int idx)
+{
+	char buf[32];
+	struct cftype *cft;
+	struct hstate *h = &hstates[idx];
+
+	/* format the size */
+	mem_fmt(buf, 32, huge_page_size(h));
+
+	/* Add the limit file */
+	cft = &h->cgroup_files_dfl[0];
+	snprintf(cft->name, MAX_CFTYPE_NAME, "%s.max", buf);
+	cft->private = MEMFILE_PRIVATE(idx, RES_LIMIT);
+	cft->seq_show = hugetlb_cgroup_read_u64_max;
+	cft->write = hugetlb_cgroup_write_dfl;
+	cft->flags = CFTYPE_NOT_ON_ROOT;
+
+	/* Add the current usage file */
+	cft = &h->cgroup_files_dfl[1];
+	snprintf(cft->name, MAX_CFTYPE_NAME, "%s.current", buf);
+	cft->private = MEMFILE_PRIVATE(idx, RES_USAGE);
+	cft->seq_show = hugetlb_cgroup_read_u64_max;
+	cft->flags = CFTYPE_NOT_ON_ROOT;
+
+	/* Add the stat file */
+	cft = &h->cgroup_files_dfl[2];
+	snprintf(cft->name, MAX_CFTYPE_NAME, "%s.stat", buf);
+	cft->seq_show = hugetlb_stat_show;
+	cft->flags = CFTYPE_NOT_ON_ROOT;
+
+	/* NULL terminate the last cft */
+	cft = &h->cgroup_files_dfl[3];
+	memset(cft, 0, sizeof(*cft));
+
+	WARN_ON(cgroup_add_dfl_cftypes(&hugetlb_cgrp_subsys,
+				       h->cgroup_files_dfl));
+}
+
+static void __init __hugetlb_cgroup_file_legacy_init(int idx)
 {
 	char buf[32];
 	struct cftype *cft;
@@ -360,38 +470,44 @@ static void __init __hugetlb_cgroup_file_init(int idx)
 	mem_fmt(buf, 32, huge_page_size(h));
 
 	/* Add the limit file */
-	cft = &h->cgroup_files[0];
+	cft = &h->cgroup_files_legacy[0];
 	snprintf(cft->name, MAX_CFTYPE_NAME, "%s.limit_in_bytes", buf);
 	cft->private = MEMFILE_PRIVATE(idx, RES_LIMIT);
 	cft->read_u64 = hugetlb_cgroup_read_u64;
-	cft->write = hugetlb_cgroup_write;
+	cft->write = hugetlb_cgroup_write_legacy;
 
 	/* Add the usage file */
-	cft = &h->cgroup_files[1];
+	cft = &h->cgroup_files_legacy[1];
 	snprintf(cft->name, MAX_CFTYPE_NAME, "%s.usage_in_bytes", buf);
 	cft->private = MEMFILE_PRIVATE(idx, RES_USAGE);
 	cft->read_u64 = hugetlb_cgroup_read_u64;
 
 	/* Add the MAX usage file */
-	cft = &h->cgroup_files[2];
+	cft = &h->cgroup_files_legacy[2];
 	snprintf(cft->name, MAX_CFTYPE_NAME, "%s.max_usage_in_bytes", buf);
 	cft->private = MEMFILE_PRIVATE(idx, RES_MAX_USAGE);
 	cft->write = hugetlb_cgroup_reset;
 	cft->read_u64 = hugetlb_cgroup_read_u64;
 
 	/* Add the failcntfile */
-	cft = &h->cgroup_files[3];
+	cft = &h->cgroup_files_legacy[3];
 	snprintf(cft->name, MAX_CFTYPE_NAME, "%s.failcnt", buf);
 	cft->private  = MEMFILE_PRIVATE(idx, RES_FAILCNT);
 	cft->write = hugetlb_cgroup_reset;
 	cft->read_u64 = hugetlb_cgroup_read_u64;
 
 	/* NULL terminate the last cft */
-	cft = &h->cgroup_files[4];
+	cft = &h->cgroup_files_legacy[4];
 	memset(cft, 0, sizeof(*cft));
 
 	WARN_ON(cgroup_add_legacy_cftypes(&hugetlb_cgrp_subsys,
-					  h->cgroup_files));
+					  h->cgroup_files_legacy));
+}
+
+static void __init __hugetlb_cgroup_file_init(int idx)
+{
+	__hugetlb_cgroup_file_dfl_init(idx);
+	__hugetlb_cgroup_file_legacy_init(idx);
 }
 
 void __init hugetlb_cgroup_file_init(void)
@@ -433,8 +549,14 @@ void hugetlb_cgroup_migrate(struct page *oldhpage, struct page *newhpage)
 	return;
 }
 
+static struct cftype hugetlb_files[] = {
+	{} /* terminate */
+};
+
 struct cgroup_subsys hugetlb_cgrp_subsys = {
 	.css_alloc	= hugetlb_cgroup_css_alloc,
 	.css_offline	= hugetlb_cgroup_css_offline,
 	.css_free	= hugetlb_cgroup_css_free,
+	.dfl_cftypes	= hugetlb_files,
+	.legacy_cftypes	= hugetlb_files,
 };
-- 
2.23.0





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