Re: [Xen-devel] [PATCH] mm: fix regression with deferred struct page init

[Juergen Gross <jgross@suse.com>]

On 25.06.19 10:25, Juergen Gross wrote:
> Gentle ping.
> 
> I'd really like to have that in 5.2 in order to avoid the regression
> introduced with 5.2-rc1.

Adding some maintainers directly...


Juergen

> 
> 
> Juergen
> 
> On 20.06.19 18:08, Juergen Gross wrote:
>> Commit 0e56acae4b4dd4a9 ("mm: initialize MAX_ORDER_NR_PAGES at a time
>> instead of doing larger sections") is causing a regression on some
>> systems when the kernel is booted as Xen dom0.
>>
>> The system will just hang in early boot.
>>
>> Reason is an endless loop in get_page_from_freelist() in case the first
>> zone looked at has no free memory. deferred_grow_zone() is always
>> returning true due to the following code snipplet:
>>
>>    /* If the zone is empty somebody else may have cleared out the zone */
>>    if (!deferred_init_mem_pfn_range_in_zone(&i, zone, &spfn, &epfn,
>>                                             first_deferred_pfn)) {
>>            pgdat->first_deferred_pfn = ULONG_MAX;
>>            pgdat_resize_unlock(pgdat, &flags);
>>            return true;
>>    }
>>
>> This in turn results in the loop as get_page_from_freelist() is
>> assuming forward progress can be made by doing some more struct page
>> initialization.
>>
>> Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
>> Fixes: 0e56acae4b4dd4a9 ("mm: initialize MAX_ORDER_NR_PAGES at a time 
>> instead of doing larger sections")
>> Suggested-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
>> Signed-off-by: Juergen Gross <jgross@suse.com>
>> ---
>>   mm/page_alloc.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index d66bc8abe0af..8e3bc949ebcc 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -1826,7 +1826,8 @@ deferred_grow_zone(struct zone *zone, unsigned 
>> int order)
>>                            first_deferred_pfn)) {
>>           pgdat->first_deferred_pfn = ULONG_MAX;
>>           pgdat_resize_unlock(pgdat, &flags);
>> -        return true;
>> +        /* Retry only once. */
>> +        return first_deferred_pfn != ULONG_MAX;
>>       }
>>       /*
>>
> 
> 
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