On 2016/3/8 23:36, Joonsoo Kim wrote: > 2016-03-08 19:45 GMT+09:00 Xishi Qiu <qiuxishi@xxxxxxxxxx>: >> On 2016/3/8 15:48, Joonsoo Kim wrote: >> >>> On Mon, Mar 07, 2016 at 01:59:12PM +0100, Vlastimil Babka wrote: >>>> On 03/07/2016 05:34 AM, Joonsoo Kim wrote: >>>>> On Fri, Mar 04, 2016 at 03:35:26PM +0800, Hanjun Guo wrote: >>>>>>> Sad to hear that. >>>>>>> >>>>>>> Could you tell me your system's MAX_ORDER and pageblock_order? >>>>>>> >>>>>> >>>>>> MAX_ORDER is 11, pageblock_order is 9, thanks for your help! >>>> >>>> I thought that CMA regions/operations (and isolation IIRC?) were >>>> supposed to be MAX_ORDER aligned exactly to prevent needing these >>>> extra checks for buddy merging. So what's wrong? >>> >>> CMA isolates MAX_ORDER aligned blocks, but, during the process, >>> partialy isolated block exists. If MAX_ORDER is 11 and >>> pageblock_order is 9, two pageblocks make up MAX_ORDER >>> aligned block and I can think following scenario because pageblock >>> (un)isolation would be done one by one. >>> >>> (each character means one pageblock. 'C', 'I' means MIGRATE_CMA, >>> MIGRATE_ISOLATE, respectively. >>> >> >> Hi Joonsoo, >> >>> CC -> IC -> II (Isolation) >> >>> II -> CI -> CC (Un-isolation) >>> >>> If some pages are freed at this intermediate state such as IC or CI, >>> that page could be merged to the other page that is resident on >>> different type of pageblock and it will cause wrong freepage count. >>> >> >> Isolation will appear when do cma alloc, so there are two following threads. >> >> C(free)C(used) -> start_isolate_page_range -> I(free)C(used) -> I(free)I(someone free it) -> undo_isolate_page_range -> C(free)C(free) >> so free cma is 2M -> 0M -> 0M -> 4M, the increased 2M was freed by someone. > > Your example is correct one but think about following one. > C(free)C(used) -> start_isolate_page_range -> I(free)C(used) -> > I(free)**C**(someone free it) -> undo_isolate_page_range -> > C(free)C(free) > > it would be 2M -> 0M -> 2M -> 6M. > When we do I(free)C(someone free it), CMA freepage is added > because it is on CMA pageblock. But, bad merging happens and > 4M buddy is made and it is in isolate buddy list. > Later, when we do undo_isolation, this 4M buddy is moved to > CMA buddy list and 4M is added to CMA freepage counter so > total is 6M. > Hi Joonsoo, I know the cause of the problem now, thank you very much. > Thanks. > > . > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>