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

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Message-Id: <1630712371.zxj5zdhheu.astroid@bobo.none>
Date:   Sat, 04 Sep 2021 09:42:00 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     Matthew Wilcox <willy@...radead.org>
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?

Excerpts from Matthew Wilcox's message of September 4, 2021 5:01 am:
> 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?

What Linus said. The patch was obviously mechanism only and more 
heuristics would need to be done (in that case you could have per inode 
hints or whatever).

> (And which way would you choose to do it now, given
> the infrastructure we have now?)

I'm not aware of anything new that would change it fundamentally.

Thanks,
Nick