From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DAC6DC43457 for ; Fri, 9 Oct 2020 14:38:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AA44E222BA for ; Fri, 9 Oct 2020 14:38:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389120AbgJIOis (ORCPT ); Fri, 9 Oct 2020 10:38:48 -0400 Received: from shelob.surriel.com ([96.67.55.147]:39214 "EHLO shelob.surriel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387978AbgJIOic (ORCPT ); Fri, 9 Oct 2020 10:38:32 -0400 Received: from imladris.surriel.com ([96.67.55.152]) by shelob.surriel.com with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94) (envelope-from ) id 1kQtXK-00076v-Lf; Fri, 09 Oct 2020 10:38:22 -0400 Message-ID: <82a7690e181cf1995e733120dad828e628cb80d9.camel@surriel.com> Subject: Re: [PATCH 0/2] mm,swap: skip swap readahead for instant IO (like zswap) From: Rik van Riel To: Andrew Morton Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel-team@fb.com, niketa@fb.com, sjenning@redhat.com, ddstreet@ieee.org, konrad.wilk@oracle.com, hannes@cmpxchg.org Date: Fri, 09 Oct 2020 10:38:22 -0400 In-Reply-To: <8b68bf5f6b041a75a62a1908214279a45722dda6.camel@surriel.com> References: <20200922020148.3261797-1-riel@surriel.com> <20200922101250.527d9e676fefbb4c8d0cd5b9@linux-foundation.org> <8b68bf5f6b041a75a62a1908214279a45722dda6.camel@surriel.com> Content-Type: multipart/signed; micalg="pgp-sha256"; protocol="application/pgp-signature"; boundary="=-k60RIuQHusUl9KWWws/D" User-Agent: Evolution 3.34.4 (3.34.4-1.fc31) MIME-Version: 1.0 Sender: riel@shelob.surriel.com Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --=-k60RIuQHusUl9KWWws/D Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Mon, 2020-10-05 at 13:32 -0400, Rik van Riel wrote: > On Tue, 2020-09-22 at 10:12 -0700, Andrew Morton wrote: > > On Mon, 21 Sep 2020 22:01:46 -0400 Rik van Riel > > wrote: > > Any quantitative testing results? >=20 > I have test results with a real workload now. >=20 > Without this patch, enabling zswap results in about an=20 > 8% increase in p99 request latency. With these patches, > the latency penalty for enabling zswap is under 1%. Never mind that. On larger tests the effect seems to disappear, probably because the logic in __swapin_nr_pages() already reduces the number of pages read ahead to 2 on workloads with lots of random access. That reduces the latency effects observed. Now we might still see some memory waste due to decompressing pages we don't need, but I have not seen any real effects from that yet, either. I think it may be time to focus on a larger memory waste with zswap: leaving the compressed copy of memory around when we decompress the memory at swapin time. More aggressively freeing the compressed memory will probably buy us more than reducing readahead. --=20 All Rights Reversed. --=-k60RIuQHusUl9KWWws/D Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- iQEzBAABCAAdFiEEKR73pCCtJ5Xj3yADznnekoTE3oMFAl+Add4ACgkQznnekoTE 3oMWOwf/Y2Os9TF60rmXZz3GfPj0PJEwiaZahgqw980IbInRx2YG3rrcnYvLUW9h 54bhIK65h/q94iDktf1y4XHEW8vkHDQalV5794DMw7ensXC97swrHaQ8s66nQgnQ TNlffRJghZgQa7ERNQ1pzDrDIlSUGqgu1a2OT0EJIlBvD5qlxEIB1k363HHpc906 md9AzXF+Rigj9AV9+6BCtb/ROGj7bbT8OMuRD19MbHBSF2SkaR9rjawkkdYMHWdd kRBlO2GYJDrO1wxBBBeqSYgI+TcH1o3vhDG1Cb3PPV4GB/BuLgORf8N8Bx1380pd 7U0KZ2FnGOYrBWeb3ufFUyIWc33/6w== =5PNd -----END PGP SIGNATURE----- --=-k60RIuQHusUl9KWWws/D--