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=-3.8 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 1F4ECC4363A for ; Mon, 5 Oct 2020 17:33:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CB1272083B for ; Mon, 5 Oct 2020 17:33:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728296AbgJERdH (ORCPT ); Mon, 5 Oct 2020 13:33:07 -0400 Received: from shelob.surriel.com ([96.67.55.147]:35418 "EHLO shelob.surriel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726727AbgJERdH (ORCPT ); Mon, 5 Oct 2020 13:33:07 -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 1kPUM6-0000l1-SW; Mon, 05 Oct 2020 13:32:58 -0400 Message-ID: <8b68bf5f6b041a75a62a1908214279a45722dda6.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: Mon, 05 Oct 2020 13:32:58 -0400 In-Reply-To: <20200922101250.527d9e676fefbb4c8d0cd5b9@linux-foundation.org> References: <20200922020148.3261797-1-riel@surriel.com> <20200922101250.527d9e676fefbb4c8d0cd5b9@linux-foundation.org> Content-Type: multipart/signed; micalg="pgp-sha256"; protocol="application/pgp-signature"; boundary="=-1HlrNNuV+v0YHd1dQ6AW" 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 --=-1HlrNNuV+v0YHd1dQ6AW Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable 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: >=20 > > Both with frontswap/zswap, and with some extremely fast IO devices, > > swap IO will be done before the "asynchronous" swap_readpage() call > > has returned. > >=20 > > In that case, doing swap readahead only wastes memory, increases > > latency, and increases the chances of needing to evict something > > more > > useful from memory. In that case, just skip swap readahead. >=20 > Any quantitative testing results? I have test results with a real workload now. 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%. Enabling zswap allows us to give the main workload a little more memory, since the spikes in memory demand caused by things like system management software no=20 longer cause large latency issues. --=20 All Rights Reversed. --=-1HlrNNuV+v0YHd1dQ6AW Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- iQEzBAABCAAdFiEEKR73pCCtJ5Xj3yADznnekoTE3oMFAl97WMoACgkQznnekoTE 3oOuNAf/VvedH4o2JVSglsPQJhfZtcQGs3NKxtf4aeYMG6zaraNif96uDsLkPXg6 FyglKUUold3TutubxTQCmlzaLg1Pzgd78Y5zjDrn1sUDgbADbIxBSYBrm9S092GE 40JpStSZilhDIQmW/FL3GdIwiKgzrHZCRacKv0PWQiXZuWm15jLMPWX6RcnrGbQI ZKqGQ031JDlyvrUuHnOKvPAj1GkjLOcRbfv8HMbREGuExhUTMmEE5JB5t+GYYkzk 0NV4kt2KWN0j2fV/h+qdXc04uVdljhb7I18ffoG4LV/lPUIRN47K+ljXwgkbVGPP H34Pi6YbUfgBwqEULfZfLxKW+BUUPw== =HycA -----END PGP SIGNATURE----- --=-1HlrNNuV+v0YHd1dQ6AW--