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From: Minchan Kim <minchan@kernel.org>
To: Matthew Wilcox <willy@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	<linux-kernel@vger.kernel.org>, <linux-arch@vger.kernel.org>,
	<sergey.senozhatsky@gmail.com>, <iamjoonsoo.kim@lge.com>,
	<ngupta@vflare.org>, <zhouxianrong@huawei.com>,
	<zhouxiyu@huawei.com>, <weidu.du@huawei.com>,
	<zhangshiming5@huawei.com>, <Mi.Sophia.Wang@huawei.com>,
	<won.ho.park@huawei.com>
Subject: Re: memfill
Date: Tue, 7 Feb 2017 13:59:48 +0900
Message-ID: <20170207045948.GB2215@bbox> (raw)
In-Reply-To: <20170206144902.GH2267@bombadil.infradead.org>

Hi Matthew,

On Mon, Feb 06, 2017 at 06:49:02AM -0800, Matthew Wilcox wrote:
> 
> [adding linux-arch to see if anyone there wants to do an optimised
> version of memfill for their CPU]
> 
> 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 would suggest:
> 
> #ifndef __HAVE_ARCH_MEMFILL
> /** 
>  * memfill - Fill a region of memory with the given value
>  * @s: Pointer to the start of the region.
>  * @v: The word to fill the region with.
>  * @n: The size of the region.
>  * 
>  * Differs from memset() in that it fills with an unsigned long instead of 
>  * a byte.  The pointer and the size must be aligned to unsigned long.
>  */
> void memfill(unsigned long *s, unsigned long v, size_t n)
> {
> 	WARN_ON_ONCE(!IS_ALIGNED(n, sizeof(v)));
> 
> 	if (likely(v == 0)) {
> 		memset(s, 0, n);
> 	} else {
> 		while (n) {
> 			*s++ = v;
> 			n -= sizeof(v);
> 		}
> 	}
> }
> EXPORT_SYMBOL(memfill);
> #endif
> 
> (I would also suggest this move to lib/string.c and architectures be
> given the opportunity to provide an optimised version of memfill).

Thanks for suggestion, Matthew!

However, I want to mention zram's performance wouldn't be sensitive
for that function because non-zero memfill would be rare.

  parent reply index

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-02-05 15:16 [PATCH v4] zram: extend zero pages to same element pages Minchan Kim
2017-02-06 14:49 ` memfill Matthew Wilcox
2017-02-07  2:47   ` memfill zhouxianrong
2017-02-07  4:59   ` Minchan Kim [this message]
2017-02-07 19:07   ` memfill James Bottomley
2017-02-08 18:04     ` memfill Matthew Wilcox
2017-02-08 21:01       ` memfill James Bottomley
2017-02-08 21:54         ` memfill Matthew Wilcox
2017-02-07  6:57 ` [PATCH v4] zram: extend zero pages to same element pages Minchan Kim
2017-02-07  9:40 ` memfill David Howells
2017-02-07 17:22   ` memfill Matthew Wilcox
2017-02-07 17:29   ` memfill David Howells
2017-02-07 19:03     ` memfill Matthew Wilcox
2017-03-11 14:56 ` memfill v2 now with ARM and x86 implementations Matthew Wilcox
2017-03-13  5:17   ` Minchan Kim

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