linux-kernel - Re: [v2 RFC PATCH 0/9] Another Approach to Use PMEM as NUMA Node

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Message-ID: <bddc3469-2984-2d32-f2cf-e1d0cc64f1e8@intel.com>
Date:   Tue, 16 Apr 2019 08:46:56 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Yang Shi <yang.shi@...ux.alibaba.com>, mgorman@...hsingularity.net,
        riel@...riel.com, hannes@...xchg.org, akpm@...ux-foundation.org,
        keith.busch@...el.com, dan.j.williams@...el.com,
        fengguang.wu@...el.com, fan.du@...el.com, ying.huang@...el.com,
        ziy@...dia.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [v2 RFC PATCH 0/9] Another Approach to Use PMEM as NUMA Node

On 4/16/19 7:39 AM, Michal Hocko wrote:
>> Strict binding also doesn't keep another app from moving the
>> memory.
> I would consider that a bug.

A bug where, though?  Certainly not in the kernel.

I'm just saying that if an app has an assumption that strict binding
means that its memory can *NEVER* move, then that assumption is simply
wrong.  It's not the guarantee that we provide.  In fact, we provide
APIs (migrate_pages() at leaset) that explicitly and intentionally break
that guarantee.

All that our NUMA APIs provide (even the strict ones) is a promise about
where newly-allocated pages will be allocated.