Re: [PATCH 4/4] (CMA_AGGRESSIVE) Update page alloc function

[Hui Zhu <teawater@gmail.com>]

On Fri, Oct 24, 2014 at 1:28 PM, Joonsoo Kim <iamjoonsoo.kim@lge.com> wrote:
> On Thu, Oct 16, 2014 at 11:35:51AM +0800, Hui Zhu wrote:
>> If page alloc function __rmqueue try to get pages from MIGRATE_MOVABLE and
>> conditions (cma_alloc_counter, cma_aggressive_free_min, cma_alloc_counter)
>> allow, MIGRATE_CMA will be allocated as MIGRATE_MOVABLE first.
>>
>> Signed-off-by: Hui Zhu <zhuhui@xiaomi.com>
>> ---
>>  mm/page_alloc.c | 42 +++++++++++++++++++++++++++++++-----------
>>  1 file changed, 31 insertions(+), 11 deletions(-)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 736d8e1..87bc326 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -65,6 +65,10 @@
>>  #include <asm/div64.h>
>>  #include "internal.h"
>>
>> +#ifdef CONFIG_CMA_AGGRESSIVE
>> +#include <linux/cma.h>
>> +#endif
>> +
>>  /* prevent >1 _updater_ of zone percpu pageset ->high and ->batch fields */
>>  static DEFINE_MUTEX(pcp_batch_high_lock);
>>  #define MIN_PERCPU_PAGELIST_FRACTION (8)
>> @@ -1189,20 +1193,36 @@ static struct page *__rmqueue(struct zone *zone, unsigned int order,
>>  {
>>       struct page *page;
>>
>> -retry_reserve:
>> +#ifdef CONFIG_CMA_AGGRESSIVE
>> +     if (cma_aggressive_switch
>> +         && migratetype == MIGRATE_MOVABLE
>> +         && atomic_read(&cma_alloc_counter) == 0
>> +         && global_page_state(NR_FREE_CMA_PAGES) > cma_aggressive_free_min
>> +                                                     + (1 << order))
>> +             migratetype = MIGRATE_CMA;
>> +#endif
>> +retry:
>
> I don't get it why cma_alloc_counter should be tested.
> When cma alloc is progress, pageblock is isolated so that pages on that
> pageblock cannot be allocated. Why should we prevent aggressive
> allocation in this case?
>

Hi Joonsoo,

Even if the pageblock is isolated in the begin of function
alloc_contig_range, it will unisolate if alloc_contig_range get some
error for example "PFNs busy".  And the cma_alloc will keep call
alloc_contig_range with another address if need.

So it will decrease the contradiction between CMA allocation in
cma_alloc and __rmqueue with  cma_alloc_counter.

Thanks,
Hui

> Thanks.
>
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