Re: How to handle TIF_MEMDIE stalls?

Tetsuo Handa
2015-02-19T15:29:49Z

Michal Hocko wrote:
> On Thu 19-02-15 13:29:14, Michal Hocko wrote:
> [...]
> > Something like the following.
> __GFP_HIGH doesn't seem to be sufficient so we would need something
> slightly else but the idea is still the same:
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 8d52ab18fe0d..2d224bbdf8e8 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2599,6 +2599,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> enum migrate_mode migration_mode = MIGRATE_ASYNC;
> bool deferred_compaction = false;
> int contended_compaction = COMPACT_CONTENDED_NONE;
> + int oom = 0;
>
> /*
> * In the slowpath, we sanity check order to avoid ever trying to
> @@ -2635,6 +2636,15 @@ retry:
> alloc_flags = gfp_to_alloc_flags(gfp_mask);
>
> /*
> + * __GFP_NOFAIL allocations cannot fail but yet the current context
> + * might be blocking resources needed by the OOM victim to terminate.
> + * Allow the caller to dive into memory reserves to succeed the
> + * allocation and break out from a potential deadlock.
> + */

We don't know how many callers will pass __GFP_NOFAIL. But if 1000
threads are doing the same operation which requires __GFP_NOFAIL
allocation with a lock held, wouldn't memory reserves deplete?

This heuristic can't continue if memory reserves depleted or
continuous pages of requested order cannot be found.

> + if (oom > 10 && (gfp_mask & __GFP_NOFAIL))
> + alloc_flags |= ALLOC_NO_WATERMARKS;
> +
> + /*
> * Find the true preferred zone if the allocation is unconstrained by
> * cpusets.
> */
> @@ -2759,6 +2769,8 @@ retry:
> goto got_pg;
> if (!did_some_progress)
> goto nopage;
> +
> + oom++;
> }
> /* Wait for some write requests to complete then retry */
> wait_iff_congested(ac->preferred_zone, BLK_RW_ASYNC, HZ/50);
> --
> Michal Hocko
> SUSE Labs