linux-kernel - Re: [PATCH] mm: simplify zone

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Message-ID: <Z_xGzAx13diuCdvv@casper.infradead.org>
Date: Mon, 14 Apr 2025 00:20:44 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Barry Song <21cnbao@...il.com>
Cc: gaoxu <gaoxu2@...or.com>, Mike Rapoport <rppt@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"surenb@...gle.com" <surenb@...gle.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	yipengxiang <yipengxiang@...or.com>
Subject: Re: [PATCH] mm: simplify zone_idx()

On Mon, Apr 14, 2025 at 09:57:26AM +1200, Barry Song wrote:
> On Sat, Apr 12, 2025 at 10:06 PM gaoxu <gaoxu2@...or.com> wrote:
> > The zone info obtained through T32 in the Android 15-6.6 system(arm64):
> > (struct zone) struct (1664 bytes,
>
> I don't have a strong opinion on whether we need `zone_idx`—I'm okay
> with having it or not. If you'd like to add it, feel free to send out
> a v2 noting that it doesn't increase the struct size. If no one
> objects, it might be a nice cleanup.

Plus it's already 1664 bytes!  And we have, what, 4 zones per NUMA node?
Growing it doesn't feel like a big deal.  Although "saves two assembly
instructions" is also not exactly a big win.  If it saved a cacheline
reference, that might be more interesting, but it seems like it's more
likely to introduce a cacheline reference than save one.  Maybe just
not worth doing?