(2013/01/10 13:26), Sha Zhengju wrote:
But this method also has its pros and cons(e.g. need lock nesting). So I doubt whether the following is able to deal with these issues all together: (CPU-A does "page stat accounting" and CPU-B does "move")CPU-A CPU-B move_lock_mem_cgroup() memcg = pc->mem_cgroup SetPageDirty(page) move_unlock_mem_cgroup() move_lock_mem_cgroup() if (PageDirty) { old_memcg->nr_dirty --; new_memcg->nr_dirty ++; } pc->mem_cgroup = new_memcg move_unlock_mem_cgroup() memcg->nr_dirty ++ For CPU-A, we save pc->mem_cgroup in a temporary variable just before SetPageDirty inside move_lock and then update stats if the page is set PG_dirty successfully. But CPU-B may do "moving" in advance that "old_memcg->nr_dirty --" will make old_memcg->nr_dirty incorrect but soon CPU-A will do "memcg->nr_dirty ++" at the heels that amend the stats. However, there is a potential problem that old_memcg->nr_dirty may be minus in a very short period but not a big issue IMHO.
IMHO, this will work. Please take care of that the recorded memcg will not be invalid pointer when you update the nr_dirty later. (Maybe RCU will protect it.) _If_ this method can handle "nesting" problem clearer and make implementation simpler, please go ahead. To be honest, I'm not sure how the code will be until seeing the patch. Hmm, why you write SetPageDirty() here rather than TestSetPageDirty().... Thanks, -Kame -- 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/
