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Date: Mon, 29 Jul 2013 15:18:36 -0400
From: KOSAKI Motohiro <kosaki.motohiro@...il.com>
To: Johannes Weiner <hannes@...xchg.org>
CC: Andrew Morton <akpm@...ux-foundation.org>,
Michal Hocko <mhocko@...e.cz>,
David Rientjes <rientjes@...gle.com>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
azurIt <azurit@...ox.sk>, linux-mm@...ck.org,
cgroups@...r.kernel.org, x86@...nel.org,
linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
kosaki.motohiro@...il.com
Subject: Re: [patch 5/6] mm: memcg: enable memcg OOM killer only for user
faults
(7/25/13 6:25 PM), 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@...xchg.org>
> ---
> include/linux/memcontrol.h | 23 +++++++++++++++++++++++
> include/linux/sched.h | 3 +++
> mm/filemap.c | 11 ++++++++++-
> mm/memcontrol.c | 2 +-
> mm/memory.c | 40 ++++++++++++++++++++++++++++++----------
> 5 files changed, 67 insertions(+), 12 deletions(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 7b4d9d7..9bb5eeb 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -125,6 +125,24 @@ 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_xchg_may_oom - toggle the memcg OOM killer for a task
> + * @p: 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_xchg_may_oom(struct task_struct *p, bool new)
> +{
> + bool old;
> +
> + old = p->memcg_oom.may_oom;
> + p->memcg_oom.may_oom = new;
> +
> + return old;
> +}
The name of xchg strongly suggest the function use compare-swap op. So, it seems
misleading name. I suggest just use "set_*" or something else. In linux kernel,
many setter functions already return old value. Don't mind.
> 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;
This ":1" makes slower but doesn't diet any memory space, right? I suggest
to use bool. If anybody need to diet in future, he may change it to bit field.
That's ok, let's stop too early and questionable micro optimization.
> diff --git a/mm/filemap.c b/mm/filemap.c
> index a6981fe..2932810 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -1617,6 +1617,7 @@ int filemap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
> struct file_ra_state *ra = &file->f_ra;
> struct inode *inode = mapping->host;
> pgoff_t offset = vmf->pgoff;
> + unsigned int may_oom;
Why don't you use bool? your mem_cgroup_xchg_may_oom() uses bool and it seems cleaner more.
> @@ -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.
> */
> + may_oom = mem_cgroup_xchg_may_oom(current, 0);
> do_async_mmap_readahead(vma, ra, file, page, offset);
> + mem_cgroup_xchg_may_oom(current, may_oom);
> } else if (!page) {
> /* No page in the page cache at all */
> + may_oom = mem_cgroup_xchg_may_oom(current, 0);
> do_sync_mmap_readahead(vma, ra, file, offset);
> + mem_cgroup_xchg_may_oom(current, may_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..5ea7b47 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)
> + WARN_ON(mem_cgroup_xchg_may_oom(current, true) == true);
Please don't assume WARN_ON never erase any code. I'm not surprised if embedded
guys replace WARN_ON with nop in future.
Thanks.
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