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Subject[patch 5/7] mm: memcg: enable memcg OOM killer only for user faults
Date
System calls and kernel faults (uaccess, gup) can handle an out of
memory situation gracefully and just return -ENOMEM.

Enable the memcg OOM killer only for user faults, where it's really
the only option available.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
include/linux/memcontrol.h | 44 ++++++++++++++++++++++++++++++++++++++++++++
include/linux/sched.h | 3 +++
mm/filemap.c | 11 ++++++++++-
mm/memcontrol.c | 2 +-
mm/memory.c | 40 ++++++++++++++++++++++++++++++----------
5 files changed, 88 insertions(+), 12 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 7b4d9d7..9c449c1 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -125,6 +125,37 @@ extern void mem_cgroup_print_oom_info(struct mem_cgroup *memcg,
extern void mem_cgroup_replace_page_cache(struct page *oldpage,
struct page *newpage);

+/**
+ * mem_cgroup_toggle_oom - toggle the memcg OOM killer for the current task
+ * @new: true to enable, false to disable
+ *
+ * Toggle whether a failed memcg charge should invoke the OOM killer
+ * or just return -ENOMEM. Returns the previous toggle state.
+ */
+static inline bool mem_cgroup_toggle_oom(bool new)
+{
+ bool old;
+
+ old = current->memcg_oom.may_oom;
+ current->memcg_oom.may_oom = new;
+
+ return old;
+}
+
+static inline void mem_cgroup_enable_oom(void)
+{
+ bool old = mem_cgroup_toggle_oom(true);
+
+ WARN_ON(old == true);
+}
+
+static inline void mem_cgroup_disable_oom(void)
+{
+ bool old = mem_cgroup_toggle_oom(false);
+
+ WARN_ON(old == false);
+}
+
#ifdef CONFIG_MEMCG_SWAP
extern int do_swap_account;
#endif
@@ -348,6 +379,19 @@ static inline void mem_cgroup_end_update_page_stat(struct page *page,
{
}

+static inline bool mem_cgroup_toggle_oom(bool new)
+{
+ return false;
+}
+
+static inline void mem_cgroup_enable_oom(void)
+{
+}
+
+static inline void mem_cgroup_disable_oom(void)
+{
+}
+
static inline void mem_cgroup_inc_page_stat(struct page *page,
enum mem_cgroup_page_stat_item idx)
{
diff --git a/include/linux/sched.h b/include/linux/sched.h
index fc09d21..4b3effc 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1398,6 +1398,9 @@ struct task_struct {
unsigned long memsw_nr_pages; /* uncharged mem+swap usage */
} memcg_batch;
unsigned int memcg_kmem_skip_account;
+ struct memcg_oom_info {
+ unsigned int may_oom:1;
+ } memcg_oom;
#endif
#ifdef CONFIG_UPROBES
struct uprobe_task *utask;
diff --git a/mm/filemap.c b/mm/filemap.c
index a6981fe..4a73e1a 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1618,6 +1618,7 @@ int filemap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
struct inode *inode = mapping->host;
pgoff_t offset = vmf->pgoff;
struct page *page;
+ bool memcg_oom;
pgoff_t size;
int ret = 0;

@@ -1626,7 +1627,11 @@ int filemap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
return VM_FAULT_SIGBUS;

/*
- * Do we have something in the page cache already?
+ * Do we have something in the page cache already? Either
+ * way, try readahead, but disable the memcg OOM killer for it
+ * as readahead is optional and no errors are propagated up
+ * the fault stack. The OOM killer is enabled while trying to
+ * instantiate the faulting page individually below.
*/
page = find_get_page(mapping, offset);
if (likely(page) && !(vmf->flags & FAULT_FLAG_TRIED)) {
@@ -1634,10 +1639,14 @@ int filemap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
* We found the page, so try async readahead before
* waiting for the lock.
*/
+ memcg_oom = mem_cgroup_toggle_oom(false);
do_async_mmap_readahead(vma, ra, file, page, offset);
+ mem_cgroup_toggle_oom(memcg_oom);
} else if (!page) {
/* No page in the page cache at all */
+ memcg_oom = mem_cgroup_toggle_oom(false);
do_sync_mmap_readahead(vma, ra, file, offset);
+ mem_cgroup_toggle_oom(memcg_oom);
count_vm_event(PGMAJFAULT);
mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);
ret = VM_FAULT_MAJOR;
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 00a7a66..30ae46a 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2614,7 +2614,7 @@ static int mem_cgroup_do_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
return CHARGE_RETRY;

/* If we don't need to call oom-killer at el, return immediately */
- if (!oom_check)
+ if (!oom_check || !current->memcg_oom.may_oom)
return CHARGE_NOMEM;
/* check OOM */
if (!mem_cgroup_handle_oom(mem_over_limit, gfp_mask, get_order(csize)))
diff --git a/mm/memory.c b/mm/memory.c
index f2ab2a8..58ef726 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3752,22 +3752,14 @@ unlock:
/*
* By the time we get here, we already hold the mm semaphore
*/
-int handle_mm_fault(struct mm_struct *mm, struct vm_area_struct *vma,
- unsigned long address, unsigned int flags)
+static int __handle_mm_fault(struct mm_struct *mm, struct vm_area_struct *vma,
+ unsigned long address, unsigned int flags)
{
pgd_t *pgd;
pud_t *pud;
pmd_t *pmd;
pte_t *pte;

- __set_current_state(TASK_RUNNING);
-
- count_vm_event(PGFAULT);
- mem_cgroup_count_vm_event(mm, PGFAULT);
-
- /* do counter updates before entering really critical section. */
- check_sync_rss_stat(current);
-
if (unlikely(is_vm_hugetlb_page(vma)))
return hugetlb_fault(mm, vma, address, flags);

@@ -3851,6 +3843,34 @@ retry:
return handle_pte_fault(mm, vma, address, pte, pmd, flags);
}

+int handle_mm_fault(struct mm_struct *mm, struct vm_area_struct *vma,
+ unsigned long address, unsigned int flags)
+{
+ int ret;
+
+ __set_current_state(TASK_RUNNING);
+
+ count_vm_event(PGFAULT);
+ mem_cgroup_count_vm_event(mm, PGFAULT);
+
+ /* do counter updates before entering really critical section. */
+ check_sync_rss_stat(current);
+
+ /*
+ * Enable the memcg OOM handling for faults triggered in user
+ * space. Kernel faults are handled more gracefully.
+ */
+ if (flags & FAULT_FLAG_USER)
+ mem_cgroup_enable_oom();
+
+ ret = __handle_mm_fault(mm, vma, address, flags);
+
+ if (flags & FAULT_FLAG_USER)
+ mem_cgroup_disable_oom();
+
+ return ret;
+}
+
#ifndef __PAGETABLE_PUD_FOLDED
/*
* Allocate page upper directory.
--
1.8.3.2


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