Messages in this thread | | | Date | Wed, 16 Dec 2015 18:29:43 +0800 | From | Xishi Qiu <> | Subject | Re: [PATCH RFC] memory-hotplug: add automatic onlining policy for the newly added memory |
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On 2015/12/16 17:17, Vitaly Kuznetsov wrote:
> Xishi Qiu <qiuxishi@huawei.com> writes: > >> On 2015/12/16 2:05, Vitaly Kuznetsov wrote: >> >>> Currently, all newly added memory blocks remain in 'offline' state unless >>> someone onlines them, some linux distributions carry special udev rules >>> like: >>> >>> SUBSYSTEM=="memory", ACTION=="add", ATTR{state}=="offline", ATTR{state}="online" >>> >>> to make this happen automatically. This is not a great solution for virtual >>> machines where memory hotplug is being used to address high memory pressure >>> situations as such onlining is slow and a userspace process doing this >>> (udev) has a chance of being killed by the OOM killer as it will probably >>> require to allocate some memory. >>> >>> Introduce default policy for the newly added memory blocks in >>> /sys/devices/system/memory/hotplug_autoonline file with two possible >>> values: "offline" (the default) which preserves the current behavior and >>> "online" which causes all newly added memory blocks to go online as >>> soon as they're added. >>> >>> Cc: Jonathan Corbet <corbet@lwn.net> >>> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> >>> Cc: Daniel Kiper <daniel.kiper@oracle.com> >>> Cc: Dan Williams <dan.j.williams@intel.com> >>> Cc: Tang Chen <tangchen@cn.fujitsu.com> >>> Cc: David Vrabel <david.vrabel@citrix.com> >>> Cc: David Rientjes <rientjes@google.com> >>> Cc: Andrew Morton <akpm@linux-foundation.org> >>> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> >>> Cc: Gu Zheng <guz.fnst@cn.fujitsu.com> >>> Cc: Xishi Qiu <qiuxishi@huawei.com> >>> Cc: Mel Gorman <mgorman@techsingularity.net> >>> Cc: "K. Y. Srinivasan" <kys@microsoft.com> >>> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> >>> --- >>> - I was able to find previous attempts to fix the issue, e.g.: >>> http://marc.info/?l=linux-kernel&m=137425951924598&w=2 >>> http://marc.info/?l=linux-acpi&m=127186488905382 >>> but I'm not completely sure why it didn't work out and the solution >>> I suggest is not 'smart enough', thus 'RFC'. >> >> + CC: >> yanxiaofeng@inspur.com >> liuchangsheng@inspur.com >> >> Hi Vitaly, >> >> Why not use udev rule? I think it can online pages automatically. >> > > Two main reasons: > 1) I remember someone saying "You never need a mouse in order to add > another mouse to the kernel" -- but we we need memory to add more > memory. Udev has a chance of being killed by the OOM killer as > performing an action will probably require to allocate some > memory. Other than that udev actions are generally slow compared to what > we can do in kernel.
Hi Vitaly,
So why we add memory when there is almost no free memory left? I think the administrator should add memory when the free memory is low or he should do something to stop free memory become worse.
> > 2) I agree with Kay that '... unconditional hotplug loop through > userspace is absolutely pointless' (https://lkml.org/lkml/2013/7/25/354). > (... and I should had add him to CC, adding now). Udev maintainers > refused to add a rule for unconditional memory onlining to udev and now > linux distros have to carry such custom rules. >
If the administrator don't know how to config the udev, he could use sysfs (echo 1 > /sys/devices/system/node/nodeXX/memoryXX/online) to online it, or write a script to do this.
Thanks, Xishi Qiu
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