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From: Matthew Wilcox <willy@infradead.org>
To: James Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Minchan Kim <minchan@kernel.org>,
	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, liw@liw.fi
Subject: Re: memfill
Date: Wed, 8 Feb 2017 10:04:47 -0800
Message-ID: <20170208180447.GO2267@bombadil.infradead.org> (raw)
In-Reply-To: <1486494454.2488.60.camel@HansenPartnership.com>

On Tue, Feb 07, 2017 at 11:07:34AM -0800, James Bottomley wrote:
> > /** 
> >  * 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.

When you say 'string fill', do you mean this?

void memfill(void *dst, size_t dsz, void *src, size_t ssz)
{
	if (ssz == 1) {
		memset(dst, *(unsigned char *)src, dsz);
	} else if (ssz == sizeof(short)) {
		memset_s(dst, *(unsigned short *)src, dsz);
	} else if (ssz == sizeof(int)) {
		memset_i(dst, *(unsigned int *)src, dsz);
	} else if (ssz == sizeof(long)) {
		memset_l(dst, *(unsigned long *)src, dsz);
	} else {
		while (dsz >= ssz) {
			memcpy(dst, src, ssz);
			dsz -= ssz;
			dst += ssz;
		}
		if (dsz)
			memcpy(dst. src. dsz);
	}
}

(with memset_[sil] being obvious, I hope).  Possibly some variation on
this to optimise compile-time constant dsz.

I have no objection to that.  Indeed, it would match Lars Wirzenius'
memfill() definition (if not implementation) which makes me quite happy.

  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   ` memfill James Bottomley
2017-02-08 18:04     ` Matthew Wilcox [this message]
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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