From: Matthew Wilcox <willy@infradead.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: mateusznosek0@gmail.com, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH] mm/page_alloc.c: Micro-optimisation Remove unnecessary branch
Date: Sun, 8 Mar 2020 04:50:07 -0700 [thread overview]
Message-ID: <20200308115007.GE31215@bombadil.infradead.org> (raw)
In-Reply-To: <20200307151542.b14131037dc44a8edcb22cad@linux-foundation.org>
On Sat, Mar 07, 2020 at 03:15:42PM -0800, Andrew Morton wrote:
> On Sat, 7 Mar 2020 23:53:35 +0100 mateusznosek0@gmail.com wrote:
> > - if (unlikely(ac.nodemask != nodemask))
> > - ac.nodemask = nodemask;
> > + ac.nodemask = nodemask;
>
> This will now unconditionally dirty the ac.nodemask cacheline, which
> means that cacheline will need to be written back. If it is truly
> unlikely that the write was needed then the thinking goes that the
> test-and-branch is worthwhile, by saving on memory traffic.
>
> At least, I assume that's why the code is the way it is.
The line immediately before this hunk is:
ac.spread_dirty_pages = false;
ac is on-stack and is only 32 bytes. I don't see a reason not to do this.
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
prev parent reply other threads:[~2020-03-08 11:50 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-07 22:53 mateusznosek0
2020-03-07 23:15 ` Andrew Morton
2020-03-08 11:50 ` Matthew Wilcox [this message]
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