On Wed, 2017-04-26 at 04:46 +0000, Naoya Horiguchi wrote: > On Wed, Apr 26, 2017 at 01:45:00PM +1000, Balbir Singh wrote: > > > > > static int delete_from_lru_cache(struct page *p) > > > > > { > > > > > + if (memcg_kmem_enabled()) > > > > > + memcg_kmem_uncharge(p, 0); > > > > > + > > > > > > > > The changelog is not quite clear, so we are uncharging a page using > > > > memcg_kmem_uncharge for a page in swap cache/page cache? > > > > > > Hi Balbir, > > > > > > Yes, in the normal page lifecycle, uncharge is done in page free time. > > > But in memory error handling case, in-use pages (i.e. swap cache and page > > > cache) are removed from normal path and they don't pass page freeing code. > > > So I think that this change is to keep the consistent charging for such a case. > > > > I agree we should uncharge, but looking at the API name, it seems to > > be for kmem pages, why are we not using mem_cgroup_uncharge()? Am I missing > > something? > > Thank you for pointing out. > Actually I had the same question and this surely looks strange. > But simply calling mem_cgroup_uncharge() here doesn't work because it > assumes that page_refcount(p) == 0, which is not true in hwpoison context. > We need some other clearer way or at least some justifying comment about > why this is ok. > We should call mem_cgroup_uncharge() after isolate_lru_page()/put_page(). We could check if page_count() is 0 or force if required (!MF_RECOVERED && !MF_DELAYED). We could even skip the VM_BUG_ON if the page is poisoned. Balbir Singh. -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>