(4/8/13 3:49 PM), Cody P Schafer wrote: > On 04/08/2013 12:26 PM, KOSAKI Motohiro wrote: >> (4/8/13 1:32 PM), Cody P Schafer wrote: >>> On 04/07/2013 08:39 AM, KOSAKI Motohiro wrote: >>>> (4/5/13 4:33 PM), Cody P Schafer wrote: >>>>> No off-cpu users of the percpu pagesets exist. >>>>> >>>>> zone_pcp_update()'s goal is to adjust the ->high and ->mark members of a >>>>> percpu pageset based on a zone's ->managed_pages. We don't need to drain >>>>> the entire percpu pageset just to modify these fields. Avoid calling >>>>> setup_pageset() (and the draining required to call it) and instead just >>>>> set the fields' values. >>>>> >>>>> This does change the behavior of zone_pcp_update() as the percpu >>>>> pagesets will not be drained when zone_pcp_update() is called (they will >>>>> end up being shrunk, not completely drained, later when a 0-order page >>>>> is freed in free_hot_cold_page()). >>>>> >>>>> Signed-off-by: Cody P Schafer <cody@xxxxxxxxxxxxxxxxxx> >>>> >>>> NAK. >>>> >>>> 1) zone_pcp_update() is only used from memory hotplug and it require page drain. >>> >>> I'm looking at this code because I'm currently working on a patchset >>> which adds another interface which modifies zone sizes, so "only used >>> from memory hotplug" is a temporary thing (unless I discover that >>> zone_pcp_update() is not intended to do what I want it to do). >> >> maybe yes, maybe no. I don't know temporary or not. However the fact is, >> you must not break anywhere. You need to look all caller always. > > Right, which is why I want to understand memory hotplug's actual > requirements. > >>>> 2) stop_machin is used for avoiding race. just removing it is insane. >>> >>> What race? Is there a cross cpu access to ->high & ->batch that makes >>> using on_each_cpu() instead of stop_machine() inappropriate? It is >>> absolutely not just being removed. >> >> OK, I missed that. however your code is still wrong. >> However you can't call free_pcppages_bulk() from interrupt context and >> then you can't use on_each_cpu() anyway. > > Given drain_pages() implementation, I find that hard to believe (It uses > on_each_cpu_mask() and eventually calls free_pcppages_bulk()). > > Can you provide a reference backing up your statement? Grr. I missed again. OK you are right. go ahead. > If this turns out to be an issue, schedule_on_each_cpu() could be an > alternative. no way. schedule_on_each_cpu() is more problematic and it should be removed in the future. schedule_on_each_cpu() can only be used when caller task don't have any lock. otherwise it may make deadlock. -- 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>