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. C(used)C(free) -> start_isolate_page_range -> C(used)I(free) -> C(someone free it)C(free) -> undo_isolate_page_range -> C(free)C(free) so free cma is 2M -> 0M -> 4M -> 4M, the increased 2M was freed by someone. so these two cases are no problem, right? Thanks, Xishi Qiu > If we don't release zone lock during whole isolation process, there > would be no problem and CMA can use that implementation. But, > isolation is used by another feature and I guess it cannot use that > kind of implementation. > > 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>