linux-kernel - Re: [PATCH 15/14] arm: Rename PMD_ORDER to PMD

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Message-ID: <YsL492bvHEo4a73M@casper.infradead.org>
Date:   Mon, 4 Jul 2022 15:28:07 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>, Mike Rapoport <rppt@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 15/14] arm: Rename PMD_ORDER to PMD_BITS

On Mon, Jul 04, 2022 at 12:32:20PM +0100, Russell King (Oracle) wrote:
> On Mon, Jul 04, 2022 at 11:48:39AM +0100, Matthew Wilcox wrote:
> > On Mon, Jul 04, 2022 at 05:32:33AM +0100, Russell King (Oracle) wrote:
> > > On Sun, Jul 03, 2022 at 10:54:49PM +0100, Matthew Wilcox wrote:
> > > > On Sun, Jul 03, 2022 at 10:16:45PM +0100, Russell King (Oracle) wrote:
> > > > > On Sun, Jul 03, 2022 at 10:14:41PM +0100, Matthew Wilcox (Oracle) wrote:
> > > > > > This is the number of bits used by a PMD entry, not the order of a PMD.
> > > > > 
> > > > > No, it's not the number of bits. A PMD entry doesn't fit in 2 or 3 bits.
> > > > > This is even more confusing.
> > > > 
> > > > Well, what is it then?  The order of something is PAGE_SIZE << n, and
> > > > that doesn't seem to be what this is.
> > > 
> > > Where is it defined that "order" means "PAGE_SIZE << n" ?
> > 
> > include/asm-generic/getorder.h: * get_order - Determine the allocation order of a memory size
> 
> I really don't care - "order" is something that is a standard term,

The word "order" has many different uses, just in mathematics alone (to
say nothing of its uses in biology, business, the military, religion,
or signal processing).

https://en.wikipedia.org/wiki/Order_(mathematics)

> and is entirely appropriate in its use in this case. The fact is,
> this use conforms to the standard term usage, not some made up
> Linux whim.

At the point where you're talking about PMD order, you're in the realm
of memory management, and using terms to mean something different from
their normal meaning within mm is only going to lead to confusion.