[PATCH v10 1/8] hugetlb_cgroup: Add hugetlb_cgroup reservation counter

Mina Almasry
2020-01-15T01:26:56Z

These counters will track hugetlb reservations rather than hugetlb
memory faulted in. This patch only adds the counter, following patches
add the charging and uncharging of the counter.

This is patch 1 of an 8 patch series.

Problem:
Currently tasks attempting to reserve more hugetlb memory than is available get
a failure at mmap/shmget time. This is thanks to Hugetlbfs Reservations [1].
However, if a task attempts to reserve hugetlb memory only more than its
hugetlb_cgroup limit allows, the kernel will allow the mmap/shmget call,
but will SIGBUS the task when it attempts to fault the memory in.

We have users hitting their hugetlb_cgroup limits and thus we've been
looking at this failure mode. We'd like to improve this behavior such that users
violating the hugetlb_cgroup limits get an error on mmap/shmget time, rather
than getting SIGBUS'd when they try to fault the excess memory in. This
gives the user an opportunity to fallback more gracefully to
non-hugetlbfs memory for example.

The underlying problem is that today's hugetlb_cgroup accounting happens
at hugetlb memory *fault* time, rather than at *reservation* time.
Thus, enforcing the hugetlb_cgroup limit only happens at fault time, and
the offending task gets SIGBUS'd.

Proposed Solution:
A new page counter named
'hugetlb.xMB.reservation_[limit|usage|max_usage]_in_bytes'. This counter has
slightly different semantics than
'hugetlb.xMB.[limit|usage|max_usage]_in_bytes':

- While usage_in_bytes tracks all *faulted* hugetlb memory,
reservation_usage_in_bytes tracks all *reserved* hugetlb memory and
hugetlb memory faulted in without a prior reservation.

- If a task attempts to reserve more memory than limit_in_bytes allows,
the kernel will allow it to do so. But if a task attempts to reserve
more memory than reservation_limit_in_bytes, the kernel will fail this
reservation.

This proposal is implemented in this patch series, with tests to verify
functionality and show the usage.

Alternatives considered:
1. A new cgroup, instead of only a new page_counter attached to
the existing hugetlb_cgroup. Adding a new cgroup seemed like a lot of code
duplication with hugetlb_cgroup. Keeping hugetlb related page counters under
hugetlb_cgroup seemed cleaner as well.

2. Instead of adding a new counter, we considered adding a sysctl that modifies
the behavior of hugetlb.xMB.[limit|usage]_in_bytes, to do accounting at
reservation time rather than fault time. Adding a new page_counter seems
better as userspace could, if it wants, choose to enforce different cgroups
differently: one via limit_in_bytes, and another via
reservation_limit_in_bytes. This could be very useful if you're
transitioning how hugetlb memory is partitioned on your system one
cgroup at a time, for example. Also, someone may find usage for both
limit_in_bytes and reservation_limit_in_bytes concurrently, and this
approach gives them the option to do so.

Testing:
- Added tests passing.
- Used libhugetlbfs for regression testing.

[1]: https://www.kernel.org/doc/html/latest/vm/hugetlbfs_reserv.html

Signed-off-by: Mina Almasry <almasrymina@google.com>

---
Changes in v10:
- Renamed reservation_* to resv.*

---
include/linux/hugetlb.h | 4 +-
mm/hugetlb_cgroup.c | 115 +++++++++++++++++++++++++++++++++++-----
2 files changed, 104 insertions(+), 15 deletions(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 1e897e4168ac1..dea6143aa0685 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -432,8 +432,8 @@ struct hstate {
unsigned int surplus_huge_pages_node[MAX_NUMNODES];
#ifdef CONFIG_CGROUP_HUGETLB
/* cgroup control files */
- struct cftype cgroup_files_dfl[5];
- struct cftype cgroup_files_legacy[5];
+ struct cftype cgroup_files_dfl[7];
+ struct cftype cgroup_files_legacy[9];
#endif
char name[HSTATE_NAME_LEN];
};
diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c
index e434b05416c68..209f9b9604d34 100644
--- a/mm/hugetlb_cgroup.c
+++ b/mm/hugetlb_cgroup.c
@@ -36,6 +36,11 @@ struct hugetlb_cgroup {
*/
struct page_counter hugepage[HUGE_MAX_HSTATE];

+ /*
+ * the counter to account for hugepage reservations from hugetlb.
+ */
+ struct page_counter reserved_hugepage[HUGE_MAX_HSTATE];
+
atomic_long_t events[HUGE_MAX_HSTATE][HUGETLB_NR_MEMORY_EVENTS];
atomic_long_t events_local[HUGE_MAX_HSTATE][HUGETLB_NR_MEMORY_EVENTS];

@@ -55,6 +60,14 @@ struct hugetlb_cgroup {

static struct hugetlb_cgroup *root_h_cgroup __read_mostly;

+static inline struct page_counter *
+hugetlb_cgroup_get_counter(struct hugetlb_cgroup *h_cg, int idx, bool reserved)
+{
+ if (reserved)
+ return &h_cg->reserved_hugepage[idx];
+ return &h_cg->hugepage[idx];
+}
+
static inline
struct hugetlb_cgroup *hugetlb_cgroup_from_css(struct cgroup_subsys_state *s)
{
@@ -295,28 +308,42 @@ void hugetlb_cgroup_uncharge_cgroup(int idx, unsigned long nr_pages,

enum {
RES_USAGE,
+ RES_RESERVATION_USAGE,
RES_LIMIT,
+ RES_RESERVATION_LIMIT,
RES_MAX_USAGE,
+ RES_RESERVATION_MAX_USAGE,
RES_FAILCNT,
+ RES_RESERVATION_FAILCNT,
};

static u64 hugetlb_cgroup_read_u64(struct cgroup_subsys_state *css,
struct cftype *cft)
{
struct page_counter *counter;
+ struct page_counter *reserved_counter;
struct hugetlb_cgroup *h_cg = hugetlb_cgroup_from_css(css);

counter = &h_cg->hugepage[MEMFILE_IDX(cft->private)];
+ reserved_counter = &h_cg->reserved_hugepage[MEMFILE_IDX(cft->private)];

switch (MEMFILE_ATTR(cft->private)) {
case RES_USAGE:
return (u64)page_counter_read(counter) * PAGE_SIZE;
+ case RES_RESERVATION_USAGE:
+ return (u64)page_counter_read(reserved_counter) * PAGE_SIZE;
case RES_LIMIT:
return (u64)counter->max * PAGE_SIZE;
+ case RES_RESERVATION_LIMIT:
+ return (u64)reserved_counter->max * PAGE_SIZE;
case RES_MAX_USAGE:
return (u64)counter->watermark * PAGE_SIZE;
+ case RES_RESERVATION_MAX_USAGE:
+ return (u64)reserved_counter->watermark * PAGE_SIZE;
case RES_FAILCNT:
return counter->failcnt;
+ case RES_RESERVATION_FAILCNT:
+ return reserved_counter->failcnt;
default:
BUG();
}
@@ -338,10 +365,16 @@ static int hugetlb_cgroup_read_u64_max(struct seq_file *seq, void *v)
1 << huge_page_order(&hstates[idx]));

switch (MEMFILE_ATTR(cft->private)) {
+ case RES_RESERVATION_USAGE:
+ counter = &h_cg->reserved_hugepage[idx];
+ /* Fall through. */
case RES_USAGE:
val = (u64)page_counter_read(counter);
seq_printf(seq, "%llu\n", val * PAGE_SIZE);
break;
+ case RES_RESERVATION_LIMIT:
+ counter = &h_cg->reserved_hugepage[idx];
+ /* Fall through. */
case RES_LIMIT:
val = (u64)counter->max;
if (val == limit)
@@ -365,6 +398,7 @@ static ssize_t hugetlb_cgroup_write(struct kernfs_open_file *of,
int ret, idx;
unsigned long nr_pages;
struct hugetlb_cgroup *h_cg = hugetlb_cgroup_from_css(of_css(of));
+ bool reserved = false;

if (hugetlb_cgroup_is_root(h_cg)) /* Can't set limit on root */
return -EINVAL;
@@ -378,9 +412,14 @@ static ssize_t hugetlb_cgroup_write(struct kernfs_open_file *of,
nr_pages = round_down(nr_pages, 1 << huge_page_order(&hstates[idx]));

switch (MEMFILE_ATTR(of_cft(of)->private)) {
+ case RES_RESERVATION_LIMIT:
+ reserved = true;
+ /* Fall through. */
case RES_LIMIT:
mutex_lock(&hugetlb_limit_mutex);
- ret = page_counter_set_max(&h_cg->hugepage[idx], nr_pages);
+ ret = page_counter_set_max(hugetlb_cgroup_get_counter(h_cg, idx,
+ reserved),
+ nr_pages);
mutex_unlock(&hugetlb_limit_mutex);
break;
default:
@@ -406,18 +445,26 @@ static ssize_t hugetlb_cgroup_reset(struct kernfs_open_file *of,
char *buf, size_t nbytes, loff_t off)
{
int ret = 0;
- struct page_counter *counter;
+ struct page_counter *counter, *reserved_counter;
struct hugetlb_cgroup *h_cg = hugetlb_cgroup_from_css(of_css(of));

counter = &h_cg->hugepage[MEMFILE_IDX(of_cft(of)->private)];
+ reserved_counter =
+ &h_cg->reserved_hugepage[MEMFILE_IDX(of_cft(of)->private)];

switch (MEMFILE_ATTR(of_cft(of)->private)) {
case RES_MAX_USAGE:
page_counter_reset_watermark(counter);
break;
+ case RES_RESERVATION_MAX_USAGE:
+ page_counter_reset_watermark(reserved_counter);
+ break;
case RES_FAILCNT:
counter->failcnt = 0;
break;
+ case RES_RESERVATION_FAILCNT:
+ reserved_counter->failcnt = 0;
+ break;
default:
ret = -EINVAL;
break;
@@ -472,7 +519,7 @@ static void __init __hugetlb_cgroup_file_dfl_init(int idx)
struct hstate *h = &hstates[idx];

/* format the size */
- mem_fmt(buf, 32, huge_page_size(h));
+ mem_fmt(buf, sizeof(buf), huge_page_size(h));

/* Add the limit file */
cft = &h->cgroup_files_dfl[0];
@@ -482,15 +529,30 @@ static void __init __hugetlb_cgroup_file_dfl_init(int idx)
cft->write = hugetlb_cgroup_write_dfl;
cft->flags = CFTYPE_NOT_ON_ROOT;

- /* Add the current usage file */
+ /* Add the reservation limit file */
cft = &h->cgroup_files_dfl[1];
+ snprintf(cft->name, MAX_CFTYPE_NAME, "%s.resv.max", buf);
+ cft->private = MEMFILE_PRIVATE(idx, RES_RESERVATION_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[2];
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 current reservation usage file */
+ cft = &h->cgroup_files_dfl[3];
+ snprintf(cft->name, MAX_CFTYPE_NAME, "%s.resv.current", buf);
+ cft->private = MEMFILE_PRIVATE(idx, RES_RESERVATION_USAGE);
+ cft->seq_show = hugetlb_cgroup_read_u64_max;
+ cft->flags = CFTYPE_NOT_ON_ROOT;
+
/* Add the events file */
- cft = &h->cgroup_files_dfl[2];
+ cft = &h->cgroup_files_dfl[4];
snprintf(cft->name, MAX_CFTYPE_NAME, "%s.events", buf);
cft->private = MEMFILE_PRIVATE(idx, 0);
cft->seq_show = hugetlb_events_show;
@@ -498,7 +560,7 @@ static void __init __hugetlb_cgroup_file_dfl_init(int idx)
cft->flags = CFTYPE_NOT_ON_ROOT;

/* Add the events.local file */
- cft = &h->cgroup_files_dfl[3];
+ cft = &h->cgroup_files_dfl[5];
snprintf(cft->name, MAX_CFTYPE_NAME, "%s.events.local", buf);
cft->private = MEMFILE_PRIVATE(idx, 0);
cft->seq_show = hugetlb_events_local_show;
@@ -507,7 +569,7 @@ static void __init __hugetlb_cgroup_file_dfl_init(int idx)
cft->flags = CFTYPE_NOT_ON_ROOT;

/* NULL terminate the last cft */
- cft = &h->cgroup_files_dfl[4];
+ cft = &h->cgroup_files_dfl[6];
memset(cft, 0, sizeof(*cft));

WARN_ON(cgroup_add_dfl_cftypes(&hugetlb_cgrp_subsys,
@@ -521,7 +583,7 @@ static void __init __hugetlb_cgroup_file_legacy_init(int idx)
struct hstate *h = &hstates[idx];

/* format the size */
- mem_fmt(buf, 32, huge_page_size(h));
+ mem_fmt(buf, sizeof(buf), huge_page_size(h));

/* Add the limit file */
cft = &h->cgroup_files_legacy[0];
@@ -530,28 +592,55 @@ static void __init __hugetlb_cgroup_file_legacy_init(int idx)
cft->read_u64 = hugetlb_cgroup_read_u64;
cft->write = hugetlb_cgroup_write_legacy;

- /* Add the usage file */
+ /* Add the reservation limit file */
cft = &h->cgroup_files_legacy[1];
+ snprintf(cft->name, MAX_CFTYPE_NAME, "%s.resv.limit_in_bytes", buf);
+ cft->private = MEMFILE_PRIVATE(idx, RES_RESERVATION_LIMIT);
+ cft->read_u64 = hugetlb_cgroup_read_u64;
+ cft->write = hugetlb_cgroup_write_legacy;
+
+ /* Add the usage file */
+ cft = &h->cgroup_files_legacy[2];
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 reservation usage file */
+ cft = &h->cgroup_files_legacy[3];
+ snprintf(cft->name, MAX_CFTYPE_NAME, "%s.resv.usage_in_bytes", buf);
+ cft->private = MEMFILE_PRIVATE(idx, RES_RESERVATION_USAGE);
+ cft->read_u64 = hugetlb_cgroup_read_u64;
+
/* Add the MAX usage file */
- cft = &h->cgroup_files_legacy[2];
+ cft = &h->cgroup_files_legacy[4];
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 MAX reservation usage file */
+ cft = &h->cgroup_files_legacy[5];
+ snprintf(cft->name, MAX_CFTYPE_NAME, "%s.resv.max_usage_in_bytes", buf);
+ cft->private = MEMFILE_PRIVATE(idx, RES_RESERVATION_MAX_USAGE);
+ cft->write = hugetlb_cgroup_reset;
+ cft->read_u64 = hugetlb_cgroup_read_u64;
+
/* Add the failcntfile */
- cft = &h->cgroup_files_legacy[3];
+ cft = &h->cgroup_files_legacy[6];
snprintf(cft->name, MAX_CFTYPE_NAME, "%s.failcnt", buf);
- cft->private = MEMFILE_PRIVATE(idx, RES_FAILCNT);
+ cft->private = MEMFILE_PRIVATE(idx, RES_FAILCNT);
+ cft->write = hugetlb_cgroup_reset;
+ cft->read_u64 = hugetlb_cgroup_read_u64;
+
+ /* Add the reservation failcntfile */
+ cft = &h->cgroup_files_legacy[7];
+ snprintf(cft->name, MAX_CFTYPE_NAME, "%s.resv.failcnt", buf);
+ cft->private = MEMFILE_PRIVATE(idx, RES_RESERVATION_FAILCNT);
cft->write = hugetlb_cgroup_reset;
cft->read_u64 = hugetlb_cgroup_read_u64;

/* NULL terminate the last cft */
- cft = &h->cgroup_files_legacy[4];
+ cft = &h->cgroup_files_legacy[8];
memset(cft, 0, sizeof(*cft));

WARN_ON(cgroup_add_legacy_cftypes(&hugetlb_cgrp_subsys,
--
2.25.0.rc1.283.g88dfdc4193-goog