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From:   Dan Williams <dan.j.williams@intel.com>
Date:   Thu, 17 Jan 2019 08:50:57 -0800
Message-ID: <CAPcyv4je0XXWjej+xM4+gidryQH=p_sevD=eL6w8f-vDQzMm3w@mail.gmail.com>
Subject: Re: [PATCH 0/4] Allow persistent memory to be used like normal RAM
To:     Jeff Moyer <jmoyer@redhat.com>
Cc:     Dave Hansen <dave.hansen@linux.intel.com>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Fengguang Wu <fengguang.wu@intel.com>,
        Dave Hansen <dave@sr71.net>,
        linux-nvdimm <linux-nvdimm@lists.01.org>,
        Takashi Iwai <tiwai@suse.de>,
        Ross Zwisler <zwisler@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux MM <linux-mm@kvack.org>, Michal Hocko <mhocko@suse.com>,
        Yaowei Bai <baiyaowei@cmss.chinamobile.com>,
        "Huang, Ying" <ying.huang@intel.com>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Borislav Petkov <bp@suse.de>
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On Thu, Jan 17, 2019 at 8:29 AM Jeff Moyer <jmoyer@redhat.com> wrote:
>
> Dave Hansen <dave.hansen@linux.intel.com> writes:
>
> > Persistent memory is cool.  But, currently, you have to rewrite
> > your applications to use it.  Wouldn't it be cool if you could
> > just have it show up in your system like normal RAM and get to
> > it like a slow blob of memory?  Well... have I got the patch
> > series for you!
>
> So, isn't that what memory mode is for?
>   https://itpeernetwork.intel.com/intel-optane-dc-persistent-memory-operating-modes/

That's a hardware cache that privately manages DRAM in front of PMEM.
It benefits from some help from software [1].

> Why do we need this code in the kernel?

This goes further and enables software managed allocation decisions
with the full DRAM + PMEM address space.

[1]: https://lore.kernel.org/lkml/154767945660.1983228.12167020940431682725.stgit@dwillia2-desk3.amr.corp.intel.com/