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SubjectRe: [RFC v1 1/2] mm/page_alloc: Prevent OOM killer from triggering if requested
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[+CC Michal Hocko]

On 07/10/2017 12:49 AM, Joel Fernandes wrote:
> Certain allocation paths such as the ftrace ring buffer allocator
> want to try hard to allocate but not trigger OOM killer and de-stabilize
> the system. Currently the ring buffer uses __GFP_NO_RETRY to prevent
> the OOM killer from triggering situation however this has an issue.
> Its possible the system is in a state where:
> a) retrying can make the allocation succeed.
> b) there's plenty of memory available in the page cache to satisfy
> the request and just retrying is needed. Even though direct reclaim
> makes progress, it still couldn't find free page from the free list.
>
> This patch adds a new GFP flag (__GFP_DONTOOM) to handle the situation
> where we want the retry behavior but still want to bail out before going
> to OOM killer if retries couldn't satisfy the allocation.

Michal recently turned __GFP_REPEAT into __GFP_RETRY_MAYFAIL [1][2]
which I think does exactly what you want. Try hard as long as
reclaim/compaction makes progress, but fail the allocation instead of
triggering OOM killer. Can you check it out? It's in mmotm/linux-next.

[1]
http://www.ozlabs.org/~akpm/mmotm/broken-out/mm-tree-wide-replace-__gfp_repeat-by-__gfp_retry_mayfail-with-more-useful-semantic.patch
[2] http://lkml.kernel.org/r/20170623085345.11304-3-mhocko@kernel.org

> Cc: Alexander Duyck <alexander.h.duyck@intel.com>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Hao Lee <haolee.swjtu@gmail.com>
> Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: linux-mm@kvack.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Joel Fernandes <joelaf@google.com>
> ---
> include/linux/gfp.h | 6 +++++-
> mm/page_alloc.c | 7 +++++++
> 2 files changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> index 4c6656f1fee7..beaabd110008 100644
> --- a/include/linux/gfp.h
> +++ b/include/linux/gfp.h
> @@ -40,6 +40,7 @@ struct vm_area_struct;
> #define ___GFP_DIRECT_RECLAIM 0x400000u
> #define ___GFP_WRITE 0x800000u
> #define ___GFP_KSWAPD_RECLAIM 0x1000000u
> +#define ___GFP_DONTOOM 0x2000000u
> #ifdef CONFIG_LOCKDEP
> #define ___GFP_NOLOCKDEP 0x2000000u
> #else
> @@ -149,6 +150,8 @@ struct vm_area_struct;
> * return NULL when direct reclaim and memory compaction have failed to allow
> * the allocation to succeed. The OOM killer is not called with the current
> * implementation.
> + *
> + * __GFP_DONTOOM: The VM implementation must not OOM if retries have exhausted.
> */
> #define __GFP_IO ((__force gfp_t)___GFP_IO)
> #define __GFP_FS ((__force gfp_t)___GFP_FS)
> @@ -158,6 +161,7 @@ struct vm_area_struct;
> #define __GFP_REPEAT ((__force gfp_t)___GFP_REPEAT)
> #define __GFP_NOFAIL ((__force gfp_t)___GFP_NOFAIL)
> #define __GFP_NORETRY ((__force gfp_t)___GFP_NORETRY)
> +#define __GFP_DONTOOM ((__force gfp_t)___GFP_DONTOOM)
>
> /*
> * Action modifiers
> @@ -188,7 +192,7 @@ struct vm_area_struct;
> #define __GFP_NOLOCKDEP ((__force gfp_t)___GFP_NOLOCKDEP)
>
> /* Room for N __GFP_FOO bits */
> -#define __GFP_BITS_SHIFT (25 + IS_ENABLED(CONFIG_LOCKDEP))
> +#define __GFP_BITS_SHIFT (26 + IS_ENABLED(CONFIG_LOCKDEP))
> #define __GFP_BITS_MASK ((__force gfp_t)((1 << __GFP_BITS_SHIFT) - 1))
>
> /*
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index bd65b60939b6..970a5c380bb6 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3908,6 +3908,13 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> if (check_retry_cpuset(cpuset_mems_cookie, ac))
> goto retry_cpuset;
>
> + /*
> + * Its possible that retries failed but we still don't want OOM
> + * killer to trigger and can just try again later.
> + */
> + if (gfp_mask & __GFP_DONTOOM)
> + goto nopage;
> +
> /* Reclaim has failed us, start killing things */
> page = __alloc_pages_may_oom(gfp_mask, order, ac, &did_some_progress);
> if (page)
>

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