Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S940575AbdDTAvg (ORCPT ); Wed, 19 Apr 2017 20:51:36 -0400 Received: from mga09.intel.com ([134.134.136.24]:3976 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S937806AbdDTAvd (ORCPT ); Wed, 19 Apr 2017 20:51:33 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.37,222,1488873600"; d="scan'208";a="1137895226" From: "Huang\, Ying" To: Johannes Weiner Cc: "Huang\, Ying" , Andrew Morton , , Subject: Re: [PATCH -mm -v9 3/3] mm, THP, swap: Enable THP swap optimization only if has compound map References: <20170419070625.19776-1-ying.huang@intel.com> <20170419070625.19776-4-ying.huang@intel.com> <20170419160029.GB3376@cmpxchg.org> Date: Thu, 20 Apr 2017 08:51:30 +0800 In-Reply-To: <20170419160029.GB3376@cmpxchg.org> (Johannes Weiner's message of "Wed, 19 Apr 2017 12:00:29 -0400") Message-ID: <87a87brje5.fsf@yhuang-dev.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1808 Lines: 50 Johannes Weiner writes: > On Wed, Apr 19, 2017 at 03:06:25PM +0800, Huang, Ying wrote: >> From: Huang Ying >> >> If there is no compound map for a THP (Transparent Huge Page), it is >> possible that the map count of some sub-pages of the THP is 0. So it >> is better to split the THP before swapping out. In this way, the >> sub-pages not mapped will be freed, and we can avoid the unnecessary >> swap out operations for these sub-pages. >> >> Cc: Johannes Weiner >> Signed-off-by: "Huang, Ying" >> --- >> mm/swap_state.c | 12 +++++++++--- >> 1 file changed, 9 insertions(+), 3 deletions(-) >> >> diff --git a/mm/swap_state.c b/mm/swap_state.c >> index 3a3217f68937..b025c9878e5e 100644 >> --- a/mm/swap_state.c >> +++ b/mm/swap_state.c >> @@ -192,9 +192,15 @@ 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); >> >> - /* cannot split, skip it */ >> - if (unlikely(PageTransHuge(page)) && !can_split_huge_page(page, NULL)) >> - return 0; >> + if (unlikely(PageTransHuge(page))) { >> + /* cannot split, skip it */ >> + if (!can_split_huge_page(page, NULL)) >> + return 0; >> + /* fallback to split huge page firstly if no PMD map */ >> + if (!compound_mapcount(page) && >> + split_huge_page_to_list(page, list)) >> + return 0; >> + } > > This looks good to me, but could you please elaborate the comment a > little bit with what you have in the changelog? Something like: > > /* > * Split pages without a PMD map right away. Chances are > * some or all of the tail pages can be freed without IO. > */ The comments look much better! Thanks! I will change it. Best Regards, Huang, Ying