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From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Matthew Wilcox <willy@infradead.org>, Minchan Kim <minchan@kernel.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, 07 Feb 2017 11:07:34 -0800
Message-ID: <1486494454.2488.60.camel@HansenPartnership.com> (raw)
In-Reply-To: <20170206144902.GH2267@bombadil.infradead.org>

On Mon, 2017-02-06 at 06:49 -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)

If we're going to do this, are you sure we wouldn't be wanting a string
fill instead of a memfill (because filling either by byte or long looks
a bit restrictive) assuming static strings that we can tell the compile
time size of, it would be easy for generic code to optimise.

James

  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   ` memfill Minchan Kim
2017-02-07 19:07   ` James Bottomley [this message]
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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