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Date:   Sun, 18 Nov 2018 17:03:00 -0800
From:   Matthew Wilcox <willy@infradead.org>
To:     Yafang Shao <laoar.shao@gmail.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>, darrick.wong@oracle.com,
        Linux MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm/filemap.c: minor optimization in write_iter file
 operation
Message-ID: <20181119010300.GD7861@bombadil.infradead.org>
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 <20181118121318.GC7861@bombadil.infradead.org>
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On Sun, Nov 18, 2018 at 11:02:19PM +0800, Yafang Shao wrote:
> On Sun, Nov 18, 2018 at 8:13 PM Matthew Wilcox <willy@infradead.org> wrote:
> > Did you check the before/after code generation with this patch applied?
> 
> Yes, I did.
> My oompiler is gcc-4.8.5, a litte old, and with CONFIG_CC_OPTIMIZE_FOR_SIZE on.
> > with gcc 8.2.0, I see no difference, indicating that the compiler already
> > makes this optimisation.
> 
> Could pls. try set CONFIG_CC_OPTIMIZE_FOR_SIZE on and then compare them again ?

Actually it was already on:

# CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE is not set
CONFIG_CC_OPTIMIZE_FOR_SIZE=y

I happened to build it in my build-tiny output tree.