linux-kernel - memfill

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Message-ID: <20170206144902.GH2267@bombadil.infradead.org>
Date:   Mon, 6 Feb 2017 06:49:02 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        sergey.senozhatsky@...il.com, iamjoonsoo.kim@....com,
        ngupta@...are.org, zhouxianrong@...wei.com, zhouxiyu@...wei.com,
        weidu.du@...wei.com, zhangshiming5@...wei.com,
        Mi.Sophia.Wang@...wei.com, won.ho.park@...wei.com
Subject: memfill


[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).