From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934083AbdKBBm2 (ORCPT ); Wed, 1 Nov 2017 21:42:28 -0400 Received: from mga05.intel.com ([192.55.52.43]:19807 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933083AbdKBBm0 (ORCPT ); Wed, 1 Nov 2017 21:42:26 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.44,331,1505804400"; d="scan'208";a="1213095957" From: "Huang\, Ying" To: Cc: , , , , , , , , , , , , , , , Subject: Re: [PATCH] mm: extend reuse_swap_page range as much as possible References: <1509533474-98584-1-git-send-email-zhouxianrong@huawei.com> Date: Thu, 02 Nov 2017 09:42:22 +0800 In-Reply-To: <1509533474-98584-1-git-send-email-zhouxianrong@huawei.com> (zhouxianrong@huawei.com's message of "Wed, 1 Nov 2017 18:51:14 +0800") Message-ID: <87tvyd4fsx.fsf@yhuang-dev.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.2 (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 writes: > From: zhouxianrong > > origanlly reuse_swap_page requires that the sum of page's > mapcount and swapcount less than or equal to one. > in this case we can reuse this page and avoid COW currently. > > now reuse_swap_page requires only that page's mapcount > less than or equal to one and the page is not dirty in > swap cache. in this case we do not care its swap count. > > the page without dirty in swap cache means that it has > been written to swap device successfully for reclaim before > and then read again on a swap fault. in this case the page > can be reused even though its swap count is greater than one > and postpone the COW on other successive accesses to the swap > cache page later rather than now. > > i did this patch test in kernel 4.4.23 with arm64 and none huge > memory. it work fine. Why do you need this? You saved copying one page from memory to memory (COW) now, at the cost of reading a page from disk to memory later? Best Regards, Huang, Ying > Signed-off-by: zhouxianrong > --- > mm/swapfile.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/mm/swapfile.c b/mm/swapfile.c > index bf91dc9..c21cf07 100644 > --- a/mm/swapfile.c > +++ b/mm/swapfile.c > @@ -1543,22 +1543,27 @@ static int page_trans_huge_map_swapcount(struct page *page, int *total_mapcount, > bool reuse_swap_page(struct page *page, int *total_map_swapcount) > { > int count, total_mapcount, total_swapcount; > + int dirty; > > VM_BUG_ON_PAGE(!PageLocked(page), page); > if (unlikely(PageKsm(page))) > return false; > + dirty = PageDirty(page); > count = page_trans_huge_map_swapcount(page, &total_mapcount, > &total_swapcount); > if (total_map_swapcount) > *total_map_swapcount = total_mapcount + total_swapcount; > - if (count == 1 && PageSwapCache(page) && > + if ((total_mapcount <= 1 && !dirty) || > + (count == 1 && PageSwapCache(page) && > (likely(!PageTransCompound(page)) || > /* The remaining swap count will be freed soon */ > - total_swapcount == page_swapcount(page))) { > + total_swapcount == page_swapcount(page)))) { > if (!PageWriteback(page)) { > page = compound_head(page); > delete_from_swap_cache(page); > SetPageDirty(page); > + if (!dirty) > + return true; > } else { > swp_entry_t entry; > struct swap_info_struct *p;