Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Thu, 02 Sep 2021 13:25:36 +1000
From:   Nicholas Piggin <npiggin@gmail.com>
Subject: Re: Is it possible to implement the per-node page cache for
 programs/libraries?
To:     Shijie Huang <shijie@amperemail.onmicrosoft.com>,
        Matthew Wilcox <willy@infradead.org>
Cc:     akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, song.bao.hua@hisilicon.com,
        torvalds@linux-foundation.org, viro@zeniv.linux.org.uk,
        Frank Wang <zwang@amperecomputing.com>
References: <a2f423cf-9413-6bc8-e4d8-92374fc0449e@amperemail.onmicrosoft.com>
        <YS7yjcqA6txFHd99@casper.infradead.org>
In-Reply-To: <YS7yjcqA6txFHd99@casper.infradead.org>
MIME-Version: 1.0
Message-Id: <1630552995.2mupnzoqzs.astroid@bobo.none>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

Excerpts from Matthew Wilcox's message of September 1, 2021 1:25 pm:
> On Wed, Sep 01, 2021 at 11:07:41AM +0800, Shijie Huang wrote:
>>     In the NUMA, we only have one page cache for each file. For the
>> program/shared libraries, the
>> remote-access delays longer then the  local-access.
>>=20
>> So, is it possible to implement the per-node page cache for
>> programs/libraries?
>=20
> At this point, we have no way to support text replication within a
> process.  So what you're suggesting (if implemented) would work for
> processes which limit themselves to a single node.  That is, if you
> have a system with CPUs 0-3 on node 0 and CPUs 4-7 on node 1, a process
> which only works on node 0 or only works on node 1 will get text on the
> appropriate node.
>=20
> If there's a process which runs on both nodes 0 and 1, there's no support
> for per-node PGDs.  So it will get a mix of pages from nodes 0 and 1,
> and that doesn't necessarily seem like a big win.  I haven't yet dived
> into how hard it would be to make mm->pgd a per-node allocation.
>=20
> I have been thinking about this a bit; one of our internal performance
> teams flagged the potential performance win to me a few months ago.
> I don't have a concrete design for text replication yet; there have been
> various attempts over the years, but none were particularly compelling.

What was not compelling about it?

https://lists.openwall.net/linux-kernel/2007/07/27/112

What are the other attempts?

Thanks,
Nick