Messages in this thread | | | Date | Mon, 08 Apr 2013 12:49:33 -0700 | From | Cody P Schafer <> | Subject | Re: [PATCH 2/3] mm/page_alloc: convert zone_pcp_update() to use on_each_cpu() instead of stop_machine() |
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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@linux.vnet.ibm.com> >>> >>> 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?
If this turns out to be an issue, schedule_on_each_cpu() could be an alternative.
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