On Fri, 2012-10-19 at 11:53 -0400, Rik van Riel wrote: > > If we do need the extra refcount, why is normal > page migration safe? :)
Its mostly a matter of how convoluted you make the code, regular page migration is about as bad as you can get Normal does: follow_page(FOLL_GET) +1 isolate_lru_page() +1 put_page() -1 ending up with a page with a single reference (for anon, or one extra each for the mapping and buffer). And while I suppose I could do a put_page() in migrate_misplaced_page() that makes the function frob the page-count depending on the return value. I always try and avoid conditional locks/refs, therefore the code ends up doing: page = vm_normal_page() if (page) { get_page() migrate_misplaced_page() put_page() } where migrate_misplaced_page() does isolate_lru_page()/putback_lru_page, and this leaves the page-count invariant. We got a ref, therefore we must put a ref, is easier than we got a ref and must put except when... -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/