linux-kernel - Re: [PATCH] mm: extend zero pages to same element pages for zram

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Message-ID: <20170203153350.GC2267@bombadil.infradead.org>
Date:   Fri, 3 Feb 2017 07:33:50 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     zhouxianrong@...wei.com
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        akpm@...ux-foundation.org, sergey.senozhatsky@...il.com,
        minchan@...nel.org, iamjoonsoo.kim@....com, ngupta@...are.org,
        Mi.Sophia.Wang@...wei.com, zhouxiyu@...wei.com,
        weidu.du@...wei.com, zhangshiming5@...wei.com,
        won.ho.park@...wei.com
Subject: Re: [PATCH] mm: extend zero pages to same element pages for zram

On Fri, Feb 03, 2017 at 04:42:27PM +0800, zhouxianrong@...wei.com wrote:
> +static inline void zram_fill_page_partial(char *ptr, unsigned int size,
> +		unsigned long value)
> +{
> +	int i;
> +	unsigned long *page;
> +
> +	if (likely(value == 0)) {
> +		memset(ptr, 0, size);
> +		return;
> +	}
> +
> +	i = ((unsigned long)ptr) % sizeof(*page);
> +	if (i) {
> +		while (i < sizeof(*page)) {
> +			*ptr++ = (value >> (i * 8)) & 0xff;
> +			--size;
> +			++i;
> +		}
> +	}
> +
> +	for (i = size / sizeof(*page); i > 0; --i) {
> +		page = (unsigned long *)ptr;
> +		*page = value;
> +		ptr += sizeof(*page);
> +		size -= sizeof(*page);
> +	}
> +
> +	for (i = 0; i < size; ++i)
> +		*ptr++ = (value >> (i * 8)) & 0xff;
> +}

You're assuming little-endian here.  I think you need to do a
cpu_to_le() here, but I don't think we have a cpu_to_leul, only
cpu_to_le64/cpu_to_le32.  So you may have some work to do ...