linux-kernel - Re: [PATCH] mm/spase: never partially remove memmap for early section

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Message-ID: <CAPcyv4ipnZ2jXd-obBk4KMGPNz4DMu0jGXFEEPCnST+A2zR+Uw@mail.gmail.com>
Date:   Tue, 23 Jun 2020 17:21:06 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Wei Yang <richard.weiyang@...ux.alibaba.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.de>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        David Hildenbrand <david@...hat.com>
Subject: Re: [PATCH] mm/spase: never partially remove memmap for early section

On Tue, Jun 23, 2020 at 2:43 AM Wei Yang
<richard.weiyang@...ux.alibaba.com> wrote:
>
> For early sections, we assumes its memmap will never be partially
> removed. But current behavior breaks this.

Where do we assume that?

The primary use case for this was mapping pmem that collides with
System-RAM in the same 128MB section. That collision will certainly be
depopulated on-demand depending on the state of the pmem device. So,
I'm not understanding the problem or the benefit of this change.