Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932725AbdD0Nhd (ORCPT ); Thu, 27 Apr 2017 09:37:33 -0400 Received: from gum.cmpxchg.org ([85.214.110.215]:47488 "EHLO gum.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751194AbdD0NhZ (ORCPT ); Thu, 27 Apr 2017 09:37:25 -0400 Date: Thu, 27 Apr 2017 09:37:09 -0400 From: Johannes Weiner To: "Huang, Ying" Cc: Minchan Kim , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrea Arcangeli , Ebru Akagunduz , Michal Hocko , Tejun Heo , Hugh Dickins , Shaohua Li , Rik van Riel , cgroups@vger.kernel.org Subject: Re: [PATCH -mm -v10 1/3] mm, THP, swap: Delay splitting THP during swap out Message-ID: <20170427133709.GA13841@cmpxchg.org> References: <20170425125658.28684-1-ying.huang@intel.com> <20170425125658.28684-2-ying.huang@intel.com> <20170427053141.GA1925@bbox> <87mvb21fz1.fsf@yhuang-dev.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87mvb21fz1.fsf@yhuang-dev.intel.com> User-Agent: Mutt/1.8.2 (2017-04-18) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1390 Lines: 37 On Thu, Apr 27, 2017 at 03:12:34PM +0800, Huang, Ying wrote: > Minchan Kim writes: > > On Tue, Apr 25, 2017 at 08:56:56PM +0800, Huang, Ying wrote: > >> @@ -178,20 +192,12 @@ int add_to_swap(struct page *page, struct list_head *list) > >> VM_BUG_ON_PAGE(!PageLocked(page), page); > >> VM_BUG_ON_PAGE(!PageUptodate(page), page); > >> > >> - entry = get_swap_page(); > >> +retry: > >> + entry = get_swap_page(page); > >> if (!entry.val) > >> - return 0; > >> - > >> - if (mem_cgroup_try_charge_swap(page, entry)) { > >> - swapcache_free(entry); > >> - return 0; > >> - } > >> - > >> - if (unlikely(PageTransHuge(page))) > >> - if (unlikely(split_huge_page_to_list(page, list))) { > >> - swapcache_free(entry); > >> - return 0; > >> - } > >> + goto fail; > > > > So, with non-SSD swap, THP page *always* get the fail to get swp_entry_t > > and retry after split the page. However, it makes unncessary get_swap_pages > > call which is not trivial. If there is no SSD swap, thp-swap out should > > be void without adding any performance overhead. > > Hmm, but I have no good idea to do it simple. :( > > For HDD swap, the device raw throughput is so low (< 100M Bps > typically), that the added overhead here will not be a big issue. Do > you agree? I fully agree. If you swap to spinning rust, an extra function call here is the least of your concern.