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Date: Mon, 13 Mar 2017 14:17:50 +0900
From: Minchan Kim <minchan@kernel.org>
To: Matthew Wilcox <willy@infradead.org>
CC: Andrew Morton <akpm@linux-foundation.org>,
        <linux-kernel@vger.kernel.org>, <sergey.senozhatsky@gmail.com>,
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        <weidu.du@huawei.com>, <zhangshiming5@huawei.com>,
        <Mi.Sophia.Wang@huawei.com>, <won.ho.park@huawei.com>
Subject: Re: memfill v2 now with ARM and x86 implementations
Message-ID: <20170313051750.GA18927@bbox>
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Hi Matthew,

On Sat, Mar 11, 2017 at 06:56:40AM -0800, Matthew Wilcox wrote:
> On Mon, Feb 06, 2017 at 12:16:44AM +0900, Minchan Kim wrote:
> > +static inline void zram_fill_page(char *ptr, unsigned long len,
> > +					unsigned long value)
> > +{
> > +	int i;
> > +	unsigned long *page = (unsigned long *)ptr;
> > +
> > +	WARN_ON_ONCE(!IS_ALIGNED(len, sizeof(unsigned long)));
> > +
> > +	if (likely(value == 0)) {
> > +		memset(ptr, 0, len);
> > +	} else {
> > +		for (i = 0; i < len / sizeof(*page); i++)
> > +			page[i] = value;
> > +	}
> > +}
> 
> I've hacked up memset32/memset64 for both ARM and x86 here:
> 
> http://git.infradead.org/users/willy/linux-dax.git/shortlog/refs/heads/memfill

Thanks for the patch.

> 
> Can you do some performance testing and see if it makes a difference?

I tested that zram is *full* with non-zero 100M dedupable data(i.e.,
it's a ideal case) on x86. With this, I see 7% enhancement.
        
        perf stat -r 10 dd if=/dev/zram0 of=/dev/null

vanilla:        0.232050465 seconds time elapsed ( +-  0.51% )
memset_l:       0.217219387 seconds time elapsed ( +-  0.07% )

I doubt it makes such benefit in read workload which a small percent
non-zero dedup data(e.g., under 3%) but it makes code simple/perform
win.

Thanks.

> 
> At this point, I'd probably ask for the first 5 patches in that git
> branch to be included, and leave out memfill and the shoddy testsuite.
> 
> I haven't actually tested either asm implementation ... only the
> C fallback.