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Subject: Re: [PATCH 06/10] mm: vmscan: demote anon DRAM pages to PMEM node
To:     Keith Busch <kbusch@kernel.org>
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        "Hansen, Dave" <dave.hansen@intel.com>,
        "Busch, Keith" <keith.busch@intel.com>,
        "Williams, Dan J" <dan.j.williams@intel.com>,
        "Wu, Fengguang" <fengguang.wu@intel.com>,
        "Du, Fan" <fan.du@intel.com>, "Huang, Ying" <ying.huang@intel.com>,
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From:   Yang Shi <yang.shi@linux.alibaba.com>
Message-ID: <599849e6-05b6-1e4d-7578-5cf8825963d2@linux.alibaba.com>
Date:   Thu, 28 Mar 2019 14:59:30 -0700
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On 3/27/19 6:08 AM, Keith Busch wrote:
> On Tue, Mar 26, 2019 at 08:41:15PM -0700, Yang Shi wrote:
>> On 3/26/19 5:35 PM, Keith Busch wrote:
>>> migration nodes have higher free capacity than source nodes. And since
>>> your attempting THP's without ever splitting them, that also requires
>>> lower fragmentation for a successful migration.
>> Yes, it is possible. However, migrate_pages() already has logic to
>> handle such case. If the target node has not enough space for migrating
>> THP in a whole, it would split THP then retry with base pages.
> Oh, you're right, my mistake on splitting. So you have a good best effort
> migrate, but I still think it can fail for legitimate reasons that should
> have a swap fallback.

Yes, it still could fail. I can't tell which way is better for now. I 
just thought scanning another round then migrating should be still 
faster than swapping off the top of my head.

Thanks,
Yang