Hi Gleb, On 10/10/2013 03:15 PM, Gleb Natapov wrote:
> On Thu, Oct 10, 2013 at 03:05:58PM +0800, chai wen wrote: >> On 10/08/2013 03:39 PM, Gleb Natapov wrote: >>> 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. >> Thank you for your clarification ! I've got it. we will still work on it. >> > Should be extremely easy. Drop FOLL_GET from GUP in async_pf_execute(). One lower question, why pinning page is not necessary here? Thanks, Gu > > -- > Gleb. > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
