Re: [PATCHv2] CMA/HOTPLUG: clear buffer-head lru before page migration

[Gioh Kim <gioh.kim@lge.com>]

2014-08-01 i??i ? 7:57, Andrew Morton i?' e,?:
> On Thu, 31 Jul 2014 11:22:35 +0900 Gioh Kim <gioh.kim@lge.com> wrote:
>
>> The previous PATCH inserts invalidate_bh_lrus() only into CMA code.
>> HOTPLUG needs also dropping bh of lru.
>> So v2 inserts invalidate_bh_lrus() into both of CMA and HOTPLUG.
>>
>>
>> ---------------------------- 8< ----------------------------
>> The bh must be free to migrate a page at which bh is mapped.
>> The reference count of bh is increased when it is installed
>> into lru so that the bh of lru must be freed before migrating the page.
>>
>> This frees every bh of lru. We could free only bh of migrating page.
>> But searching lru sometimes costs more than invalidating entire lru.
>>
>> Signed-off-by: Gioh Kim <gioh.kim@lge.com>
>> Acked-by: Michal Nazarewicz <mina86@mina86.com>
>> ---
>>   mm/memory_hotplug.c |    1 +
>>   mm/page_alloc.c     |    2 ++
>>   2 files changed, 3 insertions(+)
>>
>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index a3797d3..1c5454f 100644
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -1672,6 +1672,7 @@ repeat:
>>                  lru_add_drain_all();
>>                  cond_resched();
>>                  drain_all_pages();
>> +               invalidate_bh_lrus();
>
> Both of these calls should have a comment explaining why
> invalidate_bh_lrus() is being called.
>
>>          }
>>
>>          pfn = scan_movable_pages(start_pfn, end_pfn);
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index b99643d4..c00dedf 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -6369,6 +6369,8 @@ int alloc_contig_range(unsigned long start, unsigned long end,
>>          if (ret)
>>                  return ret;
>>
>> +       invalidate_bh_lrus();
>> +
>>          ret = __alloc_contig_migrate_range(&cc, start, end);
>>          if (ret)
>>                  goto done;
>
> I do feel that this change is likely to be beneficial, but I don't want
> to apply such a patch until I know what its effects are upon all
> alloc_contig_range() callers.  Especially hugetlb.

I'm very sorry to hear that.
How can I check the effects?


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