Re: [patch 5/7] mm: memcg: enable memcg OOM killer only for user faults

[Michal Hocko <mhocko@suse.cz>]

On Sat 03-08-13 12:59:58, Johannes Weiner wrote:
> 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>

Looks better
Acked-by: Michal Hocko <mhocko@suse.cz>

Thanks
> ---
>  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
> 

-- 
Michal Hocko
SUSE Labs

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