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SubjectRe: Is it possible to implement the per-node page cache for programs/libraries?
On Wed, Sep 01, 2021 at 04:25:01AM +0100, Matthew Wilcox wrote:
> 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.
> >
> > So, is it possible to implement the per-node page cache for
> > programs/libraries?
>
> At this point, we have no way to support text replication within a
> process. So what you're suggesting (if implemented) would work for

I created a glibc patch which can do the text replication within a process.
I will send to glibc maintainer later..
(it seems glibc does not use patches to maintain the code.)


> 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.
>
> 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,
I think we do not need the per-node PGDs.

One-PGD for one process is okay to me.

> 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.
>
> 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.
>
> By the way, the degree of performance win varies between different CPUs,
> but it's measurable on all the systems we've tested on (from three
> different vendors).
Thank you for sharing this.

Thanks
Huang Shijie

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