linux-kernel - Re: Is it possible to implement the per-node page cache for programs/libraries?

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Message-ID: <YTJxFgD0kKPs51dz@casper.infradead.org>
Date:   Fri, 3 Sep 2021 20:01:42 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Nicholas Piggin <npiggin@...il.com>
Cc:     akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org,
        Shijie Huang <shijie@...eremail.onmicrosoft.com>,
        song.bao.hua@...ilicon.com, torvalds@...ux-foundation.org,
        viro@...iv.linux.org.uk, Frank Wang <zwang@...erecomputing.com>
Subject: Re: Is it possible to implement the per-node page cache for
 programs/libraries?

On Fri, Sep 03, 2021 at 05:10:31PM +1000, Nicholas Piggin wrote:
> Excerpts from Matthew Wilcox's message of September 2, 2021 8:17 pm:
> > On Thu, Sep 02, 2021 at 01:25:36PM +1000, Nicholas Piggin wrote:
> >> > 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?
> > 
> > It wasn't merged, so clearly it wasn't compelling enough?
> 
> Ha ha. It sounded like you had some reasons you didn't find it 
> particularly compelling :P

I haven't studied it in detail, but it seems to me that your patch (from
2007!) chooses whether to store pages or pcache_desc pointers in i_pages.
Was there a reason you chose to do it that way instead of having per-node
i_mapping pointers?  (And which way would you choose to do it now, given
the infrastructure we have now?)