On Thu, Jun 23, 2011 at 07:13:54AM +0800, Nai Xia wrote: > I agree on this point. Dirty bit , young bit, is by no means accurate. Even > on 4kB pages, there is always a chance that the pte are dirty but the contents > are actually the same. Yeah, the whole optimization contains trade-offs and Just a side note: the fact the dirty bit would be set even when the data is the same is actually a pros, not a cons. If the content is the same but the page was written to, it'd trigger a copy on write short after merging the page rendering the whole exercise wasteful. The cksum plays a double role, it both "stabilizes" the unstable tree, so there's less chance of bad lookups, but it also avoids us to merge stuff that is written to frequently triggering copy on writes, and the dirty bit would also catch overwrites with the same data, something the cksum can't do. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>