Messages in this thread | | | Date | Tue, 8 Oct 2013 10:39:14 +0300 | From | Gleb Natapov <> | Subject | Re: [RFC/query] kvm async_pf anon pined pages migration |
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On Tue, Oct 08, 2013 at 02:58:22PM +0800, chai wen wrote: > On 10/02/2013 12:04 AM, chaiwen wrote: > >On 09/30/2013 08:51 PM, Gleb Natapov wrote: > >>On Mon, Sep 30, 2013 at 06:03:07PM +0800, chai wen wrote: > >>>Hi all > >>> > >>>Async page fault in kvm currently pin user pages via get_user_pages. > >>>when doing page migration,the method can be found via > >>>page->mmapping->a_ops->migratepage to offline old pages and migrate to > >>>new pages. As to anonymous page there is no file mapping but a anon_vma.So > >>>the migration will fall back to some *default* migration method.Anon pages > >>>that have been pined in memory by some reasons could be failed in the migration > >>>processing because of some reasons like ref-count checking. > >>>(or I misunderstand some thing?) > >>> > >>>Now we want to make these anon pages in async_pf can be migrated, I try some > >>>ways.But there are still many problems. The following is one that replaceing > >>>the mapping of anon page arbitrarily and doing some thing based on it. > >>>Kvm-based virtual machine can works on this patch,but have no experience of > >>>offline pages because of the limitaion of resouces.I'll check it later. > >>> > >>>I don't know weather it is a right direction of this issue. > >>>All comments/criticize are welcomed. > >>The pinning is not mandatory and can (and probably should) be dropped, but > >>pinning that is done by async page faults is short lived. What problems > >>are you seeing that warrant the complexity of handling their migration? > Hi Gleb > > As to this issue, I still have some thing not very clear. > If pages pinning is successfully holding (although not mandatory) by > async page fault. > And at the same time page migration happens because of memory > hot-remove action. > It has 120*hz timeout setting in common page offline processing, > could it fail with > these async_pf pined pages migration ? > What's your opinion about this ? If it may fail under this > circumstance, should we do > some thing on it ? > 120 seconds is more than enough time for pinning to go away, but as I said the pinning is not even necessary. Patch to remove it is welcomed.
-- Gleb.
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