Re: [PATCH 08/17] mm: page_alloc: Use word-based accesses for get/set pageblock bitmaps

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



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
--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html




[Index of Archives]     [Linux Ext4 Filesystem]     [Union Filesystem]     [Filesystem Testing]     [Ceph Users]     [Ecryptfs]     [AutoFS]     [Kernel Newbies]     [Share Photos]     [Security]     [Netfilter]     [Bugtraq]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux Cachefs]     [Reiser Filesystem]     [Linux RAID]     [Samba]     [Device Mapper]     [CEPH Development]
  Powered by Linux