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[23.128.96.18]) by mx.google.com with ESMTP id x26si18684042edr.138.2020.04.19.16.56.19; Sun, 19 Apr 2020 16:56:42 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=intel.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725987AbgDSXzT (ORCPT + 99 others); Sun, 19 Apr 2020 19:55:19 -0400 Received: from mga03.intel.com ([134.134.136.65]:11903 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725947AbgDSXzT (ORCPT ); Sun, 19 Apr 2020 19:55:19 -0400 IronPort-SDR: niSQLpUn1pK78QqGfheO+K3BM+ebwyV4YclY94gFwYa0v/Qa189HVKDvNCQlD/7mlJrDF6Q/iI 0kx1lLyNAUxw== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga003.jf.intel.com ([10.7.209.27]) by orsmga103.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Apr 2020 16:55:18 -0700 IronPort-SDR: sZ1G3kofgHfIoBQELUN/HRqZRv78d/mbOfOSsLspYbAWiigElMDYY7acOlYIDPk08UoO8NJpZc OnFXbs9/UkUA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.72,404,1580803200"; d="scan'208";a="254776055" Received: from yhuang-dev.sh.intel.com (HELO yhuang-dev) ([10.239.159.23]) by orsmga003.jf.intel.com with ESMTP; 19 Apr 2020 16:55:16 -0700 From: "Huang\, Ying" To: Andrea Righi Cc: Andrew Morton , Minchan Kim , Anchal Agarwal , , Subject: Re: [PATCH v4] mm: swap: properly update readahead statistics in unuse_pte_range() References: <20200418084705.GA147642@xps-13> Date: Mon, 20 Apr 2020 07:55:16 +0800 In-Reply-To: <20200418084705.GA147642@xps-13> (Andrea Righi's message of "Sat, 18 Apr 2020 10:47:05 +0200") Message-ID: <87o8rnt4ij.fsf@yhuang-dev.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Andrea Righi writes: > In unuse_pte_range() we blindly swap-in pages without checking if the > swap entry is already present in the swap cache. > > By doing this, the hit/miss ratio used by the swap readahead heuristic > is not properly updated and this leads to non-optimal performance during > swapoff. > > Tracing the distribution of the readahead size returned by the swap > readahead heuristic during swapoff shows that a small readahead size is > used most of the time as if we had only misses (this happens both with > cluster and vma readahead), for example: > > r::swapin_nr_pages(unsigned long offset):unsigned long:$retval > COUNT EVENT > 36948 $retval = 8 > 44151 $retval = 4 > 49290 $retval = 1 > 527771 $retval = 2 > > Checking if the swap entry is present in the swap cache, instead, allows > to properly update the readahead statistics and the heuristic behaves in > a better way during swapoff, selecting a bigger readahead size: > > r::swapin_nr_pages(unsigned long offset):unsigned long:$retval > COUNT EVENT > 1618 $retval = 1 > 4960 $retval = 2 > 41315 $retval = 4 > 103521 $retval = 8 > > In terms of swapoff performance the result is the following: > > Testing environment > =================== > > - Host: > CPU: 1.8GHz Intel Core i7-8565U (quad-core, 8MB cache) > HDD: PC401 NVMe SK hynix 512GB > MEM: 16GB > > - Guest (kvm): > 8GB of RAM > virtio block driver > 16GB swap file on ext4 (/swapfile) > > Test case > ========= > - allocate 85% of memory > - `systemctl hibernate` to force all the pages to be swapped-out to the > swap file > - resume the system > - measure the time that swapoff takes to complete: > # /usr/bin/time swapoff /swapfile > > Result (swapoff time) > ====== > 5.6 vanilla 5.6 w/ this patch > ----------- ----------------- > cluster-readahead 22.09s 12.19s > vma-readahead 18.20s 15.33s > > Conclusion > ========== > > The specific use case this patch is addressing is to improve swapoff > performance in cloud environments when a VM has been hibernated, resumed > and all the memory needs to be forced back to RAM by disabling swap. > > This change allows to better exploits the advantages of the readahead > heuristic during swapoff and this improvement allows to to speed up the > resume process of such VMs. > > Reviewed-by: "Huang, Ying" > Signed-off-by: Andrea Righi Looks good to me, Thanks! Best Regards, Huang, Ying > --- > Changes in v4: > - added a "conclusion" section in the patch description to better > explain the importance of this change (no functional changes) > > mm/swapfile.c | 12 ++++++++---- > 1 file changed, 8 insertions(+), 4 deletions(-) > > diff --git a/mm/swapfile.c b/mm/swapfile.c > index 5871a2aa86a5..f8bf926c9c8f 100644 > --- a/mm/swapfile.c > +++ b/mm/swapfile.c > @@ -1937,10 +1937,14 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd, > > pte_unmap(pte); > swap_map = &si->swap_map[offset]; > - vmf.vma = vma; > - vmf.address = addr; > - vmf.pmd = pmd; > - page = swapin_readahead(entry, GFP_HIGHUSER_MOVABLE, &vmf); > + page = lookup_swap_cache(entry, vma, addr); > + if (!page) { > + vmf.vma = vma; > + vmf.address = addr; > + vmf.pmd = pmd; > + page = swapin_readahead(entry, GFP_HIGHUSER_MOVABLE, > + &vmf); > + } > if (!page) { > if (*swap_map == 0 || *swap_map == SWAP_MAP_BAD) > goto try_next;