Yang Shi <[email protected]> writes: > On 6/30/20 5:48 PM, Huang, Ying wrote: >> Hi, Yang, >> >> Yang Shi <[email protected]> writes: >> >>>>> diff -puN mm/vmscan.c~enable-numa-demotion mm/vmscan.c >>>>> --- a/mm/vmscan.c~enable-numa-demotion 2020-06-29 16:35:01.017312549 >>>>> -0700 >>>>> +++ b/mm/vmscan.c 2020-06-29 16:35:01.023312549 -0700 >>>>> @@ -4165,9 +4165,10 @@ int node_reclaim_mode __read_mostly; >>>>> * These bit locations are exposed in the vm.zone_reclaim_mode sysctl >>>>> * ABI. New bits are OK, but existing bits can never change. >>>>> */ >>>>> -#define RECLAIM_RSVD (1<<0) /* (currently ignored/unused) */ >>>>> -#define RECLAIM_WRITE (1<<1) /* Writeout pages during reclaim */ >>>>> -#define RECLAIM_UNMAP (1<<2) /* Unmap pages during reclaim */ >>>>> +#define RECLAIM_RSVD (1<<0) /* (currently ignored/unused) */ >>>>> +#define RECLAIM_WRITE (1<<1) /* Writeout pages during reclaim */ >>>>> +#define RECLAIM_UNMAP (1<<2) /* Unmap pages during reclaim */ >>>>> +#define RECLAIM_MIGRATE (1<<3) /* Migrate pages during reclaim */ >>>>> /* >>>>> * Priority for NODE_RECLAIM. This determines the fraction of pages >>>> I found that RECLAIM_MIGRATE is defined but never referenced in the >>>> patch. >>>> >>>> If my understanding of the code were correct, shrink_do_demote_mapping() >>>> is called by shrink_page_list(), which is used by kswapd and direct >>>> reclaim. So as long as the persistent memory node is onlined, >>>> reclaim-based migration will be enabled regardless of node reclaim mode. >>> It looks so according to the code. But the intention of a new node >>> reclaim mode is to do migration on reclaim *only when* the >>> RECLAIM_MODE is enabled by the users. >>> >>> It looks the patch just clear the migration target node masks if the >>> memory is offlined. >>> >>> So, I'm supposed you need check if node_reclaim is enabled before >>> doing migration in shrink_page_list() and also need make node reclaim >>> to adopt the new mode. >> But why shouldn't we migrate in kswapd and direct reclaim? I think that >> we may need a way to control it, but shouldn't disable it >> unconditionally. > > Let me share some background. In the past discussions on LKML and last > year's LSFMM the opt-in approach was preferred since the new feature > might be not stable and mature. So the new node reclaim mode was > suggested by both Mel and Michal. I'm supposed this is still a valid > point now.
Is there any technical reason? I think the code isn't very complex. If we really worry about stable and mature, isn't it enough to provide some way to enable/disable the feature? Even for kswapd and direct reclaim? Best Regards, Huang, Ying > Once it is mature and stable enough we definitely could make it > universally preferred and default behavior. > >> >>> Please refer to >>> https://lore.kernel.org/linux-mm/[email protected]/ >>> >> Best Regards, >> Huang, Ying
