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SubjectRe: THP bug and crash on sparc64 3.8
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From: David Rientjes <rientjes@google.com>
Date: Tue, 19 Feb 2013 11:37:30 -0800 (PST)

> On Tue, 19 Feb 2013, David Miller wrote:
>
>> diff --git a/arch/sparc/mm/tsb.c b/arch/sparc/mm/tsb.c
>> index 7f64743..338b406 100644
>> --- a/arch/sparc/mm/tsb.c
>> +++ b/arch/sparc/mm/tsb.c
>> @@ -288,14 +288,13 @@ static unsigned long tsb_size_to_rss_limit(unsigned long new_size)
>> * the number of entries that the current TSB can hold at once. Currently,
>> * we trigger when the RSS hits 3/4 of the TSB capacity.
>> */
>> -void tsb_grow(struct mm_struct *mm, unsigned long tsb_index, unsigned long rss)
>> +void tsb_grow(struct mm_struct *mm, unsigned long tsb_index, unsigned long rss, gfp_t gfp)
>> {
>> unsigned long max_tsb_size = 1 * 1024 * 1024;
>> unsigned long new_size, old_size, flags;
>> struct tsb *old_tsb, *new_tsb;
>> unsigned long new_cache_index, old_cache_index;
>> unsigned long new_rss_limit;
>> - gfp_t gfp_flags;
>>
>> if (max_tsb_size > (PAGE_SIZE << MAX_ORDER))
>> max_tsb_size = (PAGE_SIZE << MAX_ORDER);
>> @@ -312,12 +311,11 @@ void tsb_grow(struct mm_struct *mm, unsigned long tsb_index, unsigned long rss)
>> new_rss_limit = ~0UL;
>>
>> retry_tsb_alloc:
>> - gfp_flags = GFP_KERNEL;
>> if (new_size > (PAGE_SIZE * 2))
>> - gfp_flags = __GFP_NOWARN | __GFP_NORETRY;
>> + gfp = __GFP_NOWARN | __GFP_NORETRY;
>
> The existing code here already looks buggy for a different reason, it
> should be gfp |= __GFP_NOWARN | __GFP_NORETRY;
>
> I was wondering if you could get away with just a simple one-liner fix
> above by doing
>
> gfp_flags = rss ? GFP_KERNEL : GFP_NOWAIT;
>
> but I agree this is more robust.

Thanks for noticing that bug. I'll probably just fix the "=" to an "|="
for now.


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