On Tue, May 06, 2014 at 10:34:49PM +0200, Peter Zijlstra wrote:
> 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.
Thanks, I'll use that.
--
Mel Gorman
SUSE Labs
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