Re: [PATCH] mm: avoid livelock on !__GFP_FS allocations

[Minchan Kim <minchan.kim@gmail.com>]

On Mon, Nov 14, 2011 at 11:04 PM, Mel Gorman <mgorman@suse.de> wrote:
> This patch seems to have gotten lost in the cracks and the discussion
> on alternatives that started here https://lkml.org/lkml/2011/10/25/24
> petered out without any alternative patches being posted. Lacking
> a viable alternative patch, I'm reposting this patch because AFAIK,
> this bug still exists.
>
> Colin Cross reported;
>
>  Under the following conditions, __alloc_pages_slowpath can loop forever:
>  gfp_mask & __GFP_WAIT is true
>  gfp_mask & __GFP_FS is false
>  reclaim and compaction make no progress
>  order <= PAGE_ALLOC_COSTLY_ORDER
>
>  These conditions happen very often during suspend and resume,
>  when pm_restrict_gfp_mask() effectively converts all GFP_KERNEL
>  allocations into __GFP_WAIT.
>
>  The oom killer is not run because gfp_mask & __GFP_FS is false,
>  but should_alloc_retry will always return true when order is less
>  than PAGE_ALLOC_COSTLY_ORDER.
>
> In his fix, he avoided retrying the allocation if reclaim made no
> progress and __GFP_FS was not set. The problem is that this would
> result in GFP_NOIO allocations failing that previously succeeded
> which would be very unfortunate.
>
> The big difference between GFP_NOIO and suspend converting GFP_KERNEL
> to behave like GFP_NOIO is that normally flushers will be cleaning
> pages and kswapd reclaims pages allowing GFP_NOIO to succeed after
> a short delay. The same does not necessarily apply during suspend as
> the storage device may be suspended.  Hence, this patch special cases
> the suspend case to fail the page allocation if reclaim cannot make
> progress. This might cause suspend to abort but that is better than
> a livelock.
>
> [mgorman@suse.de: Rework fix to be suspend specific]
> Reported-and-tested-by: Colin Cross <ccross@android.com>
> Signed-off-by: Mel Gorman <mgorman@suse.de>
> ---
>  mm/page_alloc.c |   22 ++++++++++++++++++++++
>  1 files changed, 22 insertions(+), 0 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 9dd443d..5402897 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -127,6 +127,20 @@ void pm_restrict_gfp_mask(void)
>        saved_gfp_mask = gfp_allowed_mask;
>        gfp_allowed_mask &= ~GFP_IOFS;
>  }
> +
> +static bool pm_suspending(void)
> +{
> +       if ((gfp_allowed_mask & GFP_IOFS) == GFP_IOFS)
> +               return false;
> +       return true;
> +}
> +
> +#else
> +
> +static bool pm_suspending(void)
> +{
> +       return false;
> +}
>  #endif /* CONFIG_PM_SLEEP */
>
>  #ifdef CONFIG_HUGETLB_PAGE_SIZE_VARIABLE
> @@ -2214,6 +2228,14 @@ rebalance:
>
>                        goto restart;
>                }
> +
> +               /*
> +                * Suspend converts GFP_KERNEL to __GFP_WAIT which can
> +                * prevent reclaim making forward progress without
> +                * invoking OOM. Bail if we are suspending
> +                */
> +               if (pm_suspending())
> +                       goto nopage;
>        }
>
>        /* Check if we should retry the allocation */
>


I don't have much time to look into this problem so I miss some things.
But the feeling I have a mind when I faced this problem is why we
should make another special case handling function.
Already we have such thing for hibernation - oom_killer_disabled in vm
Could we use it instead of making new branch for very special case?
Maybe It would be better to rename oom_killer_disabled with
pm_is_going or something.


-- 
Kind regards,
Minchan Kim

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