Messages in this thread | | | Subject | Re: [PATCH V7] mm: memory hot-add: memory can not be added to movable zone defaultly | From | Vlastimil Babka <> | Date | Wed, 21 Oct 2015 11:00:19 +0200 |
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On 10/21/2015 04:20 AM, Changsheng Liu wrote: > > > 在 2015/10/15 0:18, Vlastimil Babka 写道: >> On 10/12/2015 08:58 AM, Changsheng Liu wrote: >>> From: Changsheng Liu <liuchangcheng@inspur.com> >>> >>> After the user config CONFIG_MOVABLE_NODE, >>> When the memory is hot added, should_add_memory_movable() return 0 >>> because all zones including ZONE_MOVABLE are empty, >>> so the memory that was hot added will be assigned to ZONE_NORMAL >>> and ZONE_NORMAL will be created firstly. >>> But we want the whole node to be added to ZONE_MOVABLE by default. >>> >>> So we change should_add_memory_movable(): if the user config >>> CONFIG_MOVABLE_NODE and sysctl parameter hotadd_memory_as_movable is 1 >>> and the ZONE_NORMAL is empty or the pfn of the hot-added memory >>> is after the end of the ZONE_NORMAL it will always return 1 >>> and then the whole node will be added to ZONE_MOVABLE by default. >>> If we want the node to be assigned to ZONE_NORMAL, >>> we can do it as follows: >>> "echo online_kernel > /sys/devices/system/memory/memoryXXX/state" >>> >>> By the patch, the behavious of kernel is changed by sysctl, >>> user can automatically create movable memory >>> by only the following udev rule: >>> SUBSYSTEM=="memory", ACTION=="add", >>> ATTR{state}=="offline", ATTR{state}="online" > I'm sorry for replying you so late due to the busy business trip. >> So just to be clear, we are adding a new sysctl, because the existing >> movable_node kernel option, which is checked by movable_node_is_enabled(), and >> does the same thing for non-hot-added-memory (?) cannot be reused for hot-added >> memory, as that would be a potentially surprising behavior change? Correct? Then >> this should be mentioned in the changelog too, and wherever "movable_node" is >> documented should also mention the new sysctl. Personally, I would expect >> movable_node to affect hot-added memory as well, and would be surprised that it >> doesn't... > I think it can let the user decides when to use this feature. > The user can enable the feature when making the hot_added memory > of a node movable and > make the feature disable to assign the hot_added memory of the next > node to ZONE_NORMAL .
So you mean sysctl is more flexible than boot option. OK, but wasn't such flexibility already provided by "echo online_kernel" vs "echo online_movable"? It doesn't sound like a strong reason for a new sysctl? Not doing surprising behavior change maybe does...
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