[PATCH v10 3/8] hugetlb_cgroup: add reservation accounting for private mappings

Mina Almasry
2020-01-15T01:27:27Z

Normally the pointer to the cgroup to uncharge hangs off the struct
page, and gets queried when it's time to free the page. With
hugetlb_cgroup reservations, this is not possible. Because it's possible
for a page to be reserved by one task and actually faulted in by another
task.

The best place to put the hugetlb_cgroup pointer to uncharge for
reservations is in the resv_map. But, because the resv_map has different
semantics for private and shared mappings, the code patch to
charge/uncharge shared and private mappings is different. This patch
implements charging and uncharging for private mappings.

For private mappings, the counter to uncharge is in
resv_map->reservation_counter. On initializing the resv_map this is set
to NULL. On reservation of a region in private mapping, the tasks
hugetlb_cgroup is charged and the hugetlb_cgroup is placed is
resv_map->reservation_counter.

On hugetlb_vm_op_close, we uncharge resv_map->reservation_counter.

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

---

Changes in v10:
- Fixed cases where the mapping is private but cgroup accounting is disabled.
Changes in V9:
- Updated for reparenting of hugetlb reservation accounting.

---
include/linux/hugetlb.h | 10 +++++++++
include/linux/hugetlb_cgroup.h | 27 ++++++++++++++++++++++++
mm/hugetlb.c | 38 +++++++++++++++++++++++++++++++++-
mm/hugetlb_cgroup.c | 28 -------------------------
4 files changed, 74 insertions(+), 29 deletions(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index dea6143aa0685..5491932ea5758 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -46,6 +46,16 @@ struct resv_map {
long adds_in_progress;
struct list_head region_cache;
long region_cache_count;
+#ifdef CONFIG_CGROUP_HUGETLB
+ /*
+ * On private mappings, the counter to uncharge reservations is stored
+ * here. If these fields are 0, then either the mapping is shared, or
+ * cgroup accounting is disabled for this resv_map.
+ */
+ struct page_counter *reservation_counter;
+ unsigned long pages_per_hpage;
+ struct cgroup_subsys_state *css;
+#endif
};
extern struct resv_map *resv_map_alloc(void);
void resv_map_release(struct kref *ref);
diff --git a/include/linux/hugetlb_cgroup.h b/include/linux/hugetlb_cgroup.h
index eab8a70d5bcb5..8c320accefe87 100644
--- a/include/linux/hugetlb_cgroup.h
+++ b/include/linux/hugetlb_cgroup.h
@@ -25,6 +25,33 @@ struct hugetlb_cgroup;
#define HUGETLB_CGROUP_MIN_ORDER 2

#ifdef CONFIG_CGROUP_HUGETLB
+enum hugetlb_memory_event {
+ HUGETLB_MAX,
+ HUGETLB_NR_MEMORY_EVENTS,
+};
+
+struct hugetlb_cgroup {
+ struct cgroup_subsys_state css;
+
+ /*
+ * the counter to account for hugepages from hugetlb.
+ */
+ 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];
+
+ /* Handle for "hugetlb.events" */
+ struct cgroup_file events_file[HUGE_MAX_HSTATE];
+
+ /* Handle for "hugetlb.events.local" */
+ struct cgroup_file events_local_file[HUGE_MAX_HSTATE];
+};

static inline struct hugetlb_cgroup *hugetlb_cgroup_from_page(struct page *page,
bool reserved)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 62a4cf3db4090..f1b63946ee95c 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -666,6 +666,17 @@ struct resv_map *resv_map_alloc(void)
INIT_LIST_HEAD(&resv_map->regions);

resv_map->adds_in_progress = 0;
+#ifdef CONFIG_CGROUP_HUGETLB
+ /*
+ * Initialize these to 0. On shared mappings, 0's here indicate these
+ * fields don't do cgroup accounting. On private mappings, these will be
+ * re-initialized to the proper values, to indicate that hugetlb cgroup
+ * reservations are to be un-charged from here.
+ */
+ resv_map->reservation_counter = NULL;
+ resv_map->pages_per_hpage = 0;
+ resv_map->css = NULL;
+#endif

INIT_LIST_HEAD(&resv_map->region_cache);
list_add(&rg->link, &resv_map->region_cache);
@@ -3194,7 +3205,11 @@ static void hugetlb_vm_op_close(struct vm_area_struct *vma)

reserve = (end - start) - region_count(resv, start, end);

- kref_put(&resv->refs, resv_map_release);
+#ifdef CONFIG_CGROUP_HUGETLB
+ hugetlb_cgroup_uncharge_counter(resv->reservation_counter,
+ (end - start) * resv->pages_per_hpage,
+ resv->css);
+#endif

if (reserve) {
/*
@@ -3204,6 +3219,8 @@ static void hugetlb_vm_op_close(struct vm_area_struct *vma)
gbl_reserve = hugepage_subpool_put_pages(spool, reserve);
hugetlb_acct_memory(h, -gbl_reserve);
}
+
+ kref_put(&resv->refs, resv_map_release);
}

static int hugetlb_vm_op_split(struct vm_area_struct *vma, unsigned long addr)
@@ -4550,6 +4567,7 @@ int hugetlb_reserve_pages(struct inode *inode,
struct hstate *h = hstate_inode(inode);
struct hugepage_subpool *spool = subpool_inode(inode);
struct resv_map *resv_map;
+ struct hugetlb_cgroup *h_cg;
long gbl_reserve;

/* This should never happen */
@@ -4583,12 +4601,30 @@ int hugetlb_reserve_pages(struct inode *inode,
chg = region_chg(resv_map, from, to);

} else {
+ /* Private mapping. */
resv_map = resv_map_alloc();
if (!resv_map)
return -ENOMEM;

chg = to - from;

+ if (hugetlb_cgroup_charge_cgroup(hstate_index(h),
+ chg * pages_per_huge_page(h),
+ &h_cg, true)) {
+ kref_put(&resv_map->refs, resv_map_release);
+ return -ENOMEM;
+ }
+
+#ifdef CONFIG_CGROUP_HUGETLB
+ /*
+ * Since this branch handles private mappings, we attach the
+ * counter to uncharge for this reservation off resv_map.
+ */
+ resv_map->reservation_counter =
+ &h_cg->reserved_hugepage[hstate_index(h)];
+ resv_map->pages_per_hpage = pages_per_huge_page(h);
+#endif
+
set_vma_resv_map(vma, resv_map);
set_vma_resv_flags(vma, HPAGE_RESV_OWNER);
}
diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c
index c434f69f38354..ddfdf19a9ad35 100644
--- a/mm/hugetlb_cgroup.c
+++ b/mm/hugetlb_cgroup.c
@@ -23,34 +23,6 @@
#include <linux/hugetlb.h>
#include <linux/hugetlb_cgroup.h>

-enum hugetlb_memory_event {
- HUGETLB_MAX,
- HUGETLB_NR_MEMORY_EVENTS,
-};
-
-struct hugetlb_cgroup {
- struct cgroup_subsys_state css;
-
- /*
- * the counter to account for hugepages from hugetlb.
- */
- 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];
-
- /* Handle for "hugetlb.events" */
- struct cgroup_file events_file[HUGE_MAX_HSTATE];
-
- /* Handle for "hugetlb.events.local" */
- struct cgroup_file events_local_file[HUGE_MAX_HSTATE];
-};
-
#define MEMFILE_PRIVATE(x, val) (((x) << 16) | (val))
#define MEMFILE_IDX(val) (((val) >> 16) & 0xffff)
#define MEMFILE_ATTR(val) ((val) & 0xffff)
--
2.25.0.rc1.283.g88dfdc4193-goog