From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752084AbcBYWf4 (ORCPT ); Thu, 25 Feb 2016 17:35:56 -0500 Received: from mx1.redhat.com ([209.132.183.28]:45529 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751015AbcBYWfz (ORCPT ); Thu, 25 Feb 2016 17:35:55 -0500 Message-ID: <1456439750.15821.97.camel@redhat.com> Subject: Re: [RFC v5 0/3] mm: make swapin readahead to gain more thp performance From: Rik van Riel To: Hugh Dickins , Ebru Akagunduz Cc: Andrew Morton , linux-mm@kvack.org, kirill.shutemov@linux.intel.com, n-horiguchi@ah.jp.nec.com, aarcange@redhat.com, iamjoonsoo.kim@lge.com, xiexiuqi@huawei.com, gorcunov@openvz.org, linux-kernel@vger.kernel.org, mgorman@suse.de, rientjes@google.com, vbabka@suse.cz, aneesh.kumar@linux.vnet.ibm.com, hannes@cmpxchg.org, mhocko@suse.cz, boaz@plexistor.com, raindel@mellanox.com Date: Thu, 25 Feb 2016 17:35:50 -0500 In-Reply-To: References: <1442259105-4420-1-git-send-email-ebru.akagunduz@gmail.com> <20150914144106.ee205c3ae3f4ec0e5202c9fe@linux-foundation.org> Content-Type: multipart/signed; micalg="pgp-sha1"; protocol="application/pgp-signature"; boundary="=-074UBnQQ639I/tHqz/QM" Mime-Version: 1.0 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Thu, 25 Feb 2016 22:35:55 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --=-074UBnQQ639I/tHqz/QM Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, 2016-02-24 at 23:36 -0800, Hugh Dickins wrote: >=C2=A0 > Doesn't this imply that __collapse_huge_page_swapin() will initiate > all > the necessary swapins for a THP, then (given the > FAULT_FLAG_ALLOW_RETRY) > not wait for them to complete, so khugepaged will give up on that > extent > and move on to another; then after another full circuit of all the > mms > it needs to examine, it will arrive back at this extent and build a > THP > from the swapins it arranged last time. >=20 > Which may work well when a system transitions from busy+swappingout > to idle+swappingin, but isn't that rather a special case?=C2=A0 It feels > (meaning, I've not measured at all) as if the inbetween busyish case > will waste a lot of I/O and memory on swapins that have to be > discarded > again before khugepaged has made its sedate way back to slotting them > in. >=C2=A0 There may be a fairly simple way to prevent that from becoming an issue. When khugepaged wakes up, it can check the PGSWPOUT or even the PGSTEAL_* stats for the system, and skip swapin readahead if there was swapout activity (or any page reclaim activity?) since the time it last ran. That way the swapin readahead will do its thing when transitioning from busy + swapout to idle + swapin, but not while the system is under permanent memory pressure. Am I forgetting anything obvious? Is this too aggressive? Not aggressive enough? Could PGPGOUT + PGSWPOUT be a useful in-between between just PGSWPOUT or PGSTEAL_*? --=C2=A0 All rights reversed --=-074UBnQQ639I/tHqz/QM Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQEcBAABAgAGBQJWz4HGAAoJEM553pKExN6DDK4H/3bbdh3MuvAyY/KD/HtKXDqw 9bz98E5L6kjgaSkCUaZmC3jq3U4BoBATu169W+aQTyikMgyoPXuBzkhEf3aeryEx vYfA10y9UD02WbxW0rk6RAChFdk5OWLSGz57JHK2a+mPn36Vjiz9XaSPkBpiHP7z CylmEliSeIElGzNdbIqIgrR5ZJKHdezIxmo9V0oq3U3z4b1+rLvBHrzdPOrLKxpQ KsPwUn2uk8ski6LTrMoBuFdOoDbXotOABXZgrAzJuTrqA8Z/gLhhuwBerUq0N8YW zKnBniX6SDSXCmiqSonl1kAoTmLGL73saDqnul9F8GRDSgW1k3Z99sf2ORmzgYE= =rGAk -----END PGP SIGNATURE----- --=-074UBnQQ639I/tHqz/QM--