linux-kernel - Re: [PATCH v4 00/25] Page folios

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20210315115501.7rmzaan2hxsqowgq@box>
Date:   Mon, 15 Mar 2021 14:55:01 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Hugh Dickins <hughd@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v4 00/25] Page folios

On Sat, Mar 13, 2021 at 07:09:01PM -0800, Hugh Dickins wrote:
> On Sat, 13 Mar 2021, Andrew Morton wrote:
> > On Fri,  5 Mar 2021 04:18:36 +0000 "Matthew Wilcox (Oracle)" <willy@...radead.org> wrote:
> > 
> > > Our type system does not currently distinguish between tail pages and
> > > head or single pages.  This is a problem because we call compound_head()
> > > multiple times (and the compiler cannot optimise it out), bloating the
> > > kernel.  It also makes programming hard as it is often unclear whether
> > > a function operates on an individual page, or an entire compound page.
> > > 
> > > This patch series introduces the struct folio, which is a type that
> > > represents an entire compound page.  This initial set reduces the kernel
> > > size by approximately 6kB, although its real purpose is adding
> > > infrastructure to enable further use of the folio.
> > 
> > Geeze it's a lot of noise.  More things to remember and we'll forever
> > have a mismash of `page' and `folio' and code everywhere converting
> > from one to the other.  Ongoing addition of folio
> > accessors/manipulators to overlay the existing page
> > accessors/manipulators, etc.
> > 
> > It's unclear to me that it's all really worth it.  What feedback have
> > you seen from others?
> 
> My own feeling and feedback have been much like yours.
> 
> I don't get very excited by type safety at this level; and although
> I protested back when all those compound_head()s got tucked into the
> *PageFlag() functions, the text size increase was not very much, and
> I never noticed any adverse performance reports.
> 
> To me, it's distraction, churn and friction, ongoing for years; but
> that's just me, and I'm resigned to the possibility that it will go in.
> Matthew is not alone in wanting to pursue it: let others speak.

I'm with Matthew on this. I would really want to drop the number of places
where we call compoud_head(). I hope we can get rid of the page flag
policy hack I made.

-- 
 Kirill A. Shutemov