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

[Minchan Kim]

On Mon, Nov 14, 2011 at 11:04 PM, Mel Gorman <mgorman@xxxxxxx> 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;
>
> ÂUnder the following conditions, __alloc_pages_slowpath can loop forever:
> Âgfp_mask & __GFP_WAIT is true
> Âgfp_mask & __GFP_FS is false
> Âreclaim and compaction make no progress
> Âorder <= PAGE_ALLOC_COSTLY_ORDER
>
> ÂThese conditions happen very often during suspend and resume,
> Âwhen pm_restrict_gfp_mask() effectively converts all GFP_KERNEL
> Âallocations into __GFP_WAIT.
>
> ÂThe oom killer is not run because gfp_mask & __GFP_FS is false,
> Âbut should_alloc_retry will always return true when order is less
> Âthan 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. ÂHence, 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@xxxxxxx: Rework fix to be suspend specific]
> Reported-and-tested-by: Colin Cross <ccross@xxxxxxxxxxx>
> Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
> ---
> Âmm/page_alloc.c | Â 22 ++++++++++++++++++++++
> Â1 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)
> Â Â Â Âsaved_gfp_mask = gfp_allowed_mask;
> Â Â Â Âgfp_allowed_mask &= ~GFP_IOFS;
> Â}
> +
> +static bool pm_suspending(void)
> +{
> + Â Â Â if ((gfp_allowed_mask & GFP_IOFS) == GFP_IOFS)
> + Â Â Â Â Â Â Â return false;
> + Â Â Â return true;
> +}
> +
> +#else
> +
> +static bool pm_suspending(void)
> +{
> + Â Â Â return false;
> +}
> Â#endif /* CONFIG_PM_SLEEP */
>
> Â#ifdef CONFIG_HUGETLB_PAGE_SIZE_VARIABLE
> @@ -2214,6 +2228,14 @@ rebalance:
>
> Â Â Â Â Â Â Â Â Â Â Â Âgoto restart;
> Â Â Â Â Â Â Â Â}
> +
> + Â Â Â Â Â Â Â /*
> + Â Â Â Â Â Â Â Â* Suspend converts GFP_KERNEL to __GFP_WAIT which can
> + Â Â Â Â Â Â Â Â* prevent reclaim making forward progress without
> + Â Â Â Â Â Â Â Â* invoking OOM. Bail if we are suspending
> + Â Â Â Â Â Â Â Â*/
> + Â Â Â Â Â Â Â if (pm_suspending())
> + Â Â Â Â Â Â Â Â Â Â Â goto nopage;
> Â Â Â Â}
>
> Â Â Â Â/* 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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