On Thu, May 01, 2014 at 09:44:39AM +0100, Mel Gorman wrote:
> +void set_pfnblock_flags_group(struct page *page, unsigned long flags,
> + unsigned long end_bitidx,
> + unsigned long nr_flag_bits,
> + unsigned long mask)
> {
> struct zone *zone;
> unsigned long *bitmap;
> + unsigned long pfn, bitidx, word_bitidx;
> + unsigned long old_word, new_word;
> +
> + BUILD_BUG_ON(NR_PAGEBLOCK_BITS != 4);
>
> zone = page_zone(page);
> pfn = page_to_pfn(page);
> bitmap = get_pageblock_bitmap(zone, pfn);
> bitidx = pfn_to_bitidx(zone, pfn);
> + word_bitidx = bitidx / BITS_PER_LONG;
> + bitidx &= (BITS_PER_LONG-1);
> +
> VM_BUG_ON_PAGE(!zone_spans_pfn(zone, pfn), page);
>
> + bitidx += end_bitidx;
> + mask <<= (BITS_PER_LONG - bitidx - 1);
> + flags <<= (BITS_PER_LONG - bitidx - 1);
> +
> + do {
> + old_word = ACCESS_ONCE(bitmap[word_bitidx]);
> + new_word = (old_word & ~mask) | flags;
> + } while (cmpxchg(&bitmap[word_bitidx], old_word, new_word) != old_word);
> }
You could write it like:
word = ACCESS_ONCE(bitmap[word_bitidx]);
for (;;) {
old_word = cmpxchg(&bitmap[word_bitidx], word, (word & ~mask) | flags);
if (word == old_word);
break;
word = old_word;
}
It has a slightly tighter loop by avoiding the read being included.
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