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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 3D437C433DF for ; Thu, 4 Jun 2020 16:37:03 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id E7F6920738 for ; Thu, 4 Jun 2020 16:37:02 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="mEjqFFkb" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E7F6920738 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 947C680007; Thu, 4 Jun 2020 12:37:02 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 8F8FD8E0006; Thu, 4 Jun 2020 12:37:02 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 80F3680007; Thu, 4 Jun 2020 12:37:02 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0153.hostedemail.com [216.40.44.153]) by kanga.kvack.org (Postfix) with ESMTP id 68B6D8E0006 for ; Thu, 4 Jun 2020 12:37:02 -0400 (EDT) Received: from smtpin04.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 20EDE1807CF92 for ; Thu, 4 Jun 2020 16:37:02 +0000 (UTC) X-FDA: 76892083884.04.milk78_5a7504ef87211 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin04.hostedemail.com (Postfix) with ESMTP id EC53180FD296 for ; Thu, 4 Jun 2020 16:37:01 +0000 (UTC) X-HE-Tag: milk78_5a7504ef87211 X-Filterd-Recvd-Size: 5393 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) by imf45.hostedemail.com (Postfix) with ESMTP for ; Thu, 4 Jun 2020 16:37:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=RCZnN0syAW3t9QwdLXO30GKp8cwgBcfJPzlUa/+XJqA=; b=mEjqFFkbAld3kjvhONwEWY/Fgl B5MRzmvxEZ+jHliUPauElMi/44BLdQpMSXbnLe8JX1+Jkz8QbrDHg/aAsHUqL1NbIeWCwXVcbjOMv OpWCyUB0VCllD8/82AElq6xkYcEP/VzFKl6vESQlf09WefpZaIpwZF6pbN4XKzS8+l3fTOS7j1FOn 8D1O/KHsNCmSF3aONJa0K86q6y7YS4vlFiiP4y6tvp6EF5JYT0dmmA4gpqQodL8bO4BjJHH9gjjp5 mkSbCbj6qzY/wW//hiDNQK7JXrUKPFilThjtkS/GMoE67ioqq5NMKcgRYH1n5Tgf+K6q4WixsaWhI zt5WylZw==; Received: from willy by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1jgsrR-0005D8-Ps; Thu, 04 Jun 2020 16:36:57 +0000 Date: Thu, 4 Jun 2020 09:36:57 -0700 From: Matthew Wilcox To: Zi Yan Cc: Anshuman Khandual , linux-mm@kvack.org, hughd@google.com, daniel.m.jordan@oracle.com, Naoya Horiguchi , John Hubbard , Andrew Morton , linux-kernel@vger.kernel.org Subject: Re: [PATCH V2] mm/vmstat: Add events for THP migration without split Message-ID: <20200604163657.GV19604@bombadil.infradead.org> References: <1591243245-23052-1-git-send-email-anshuman.khandual@arm.com> <20200604113421.GU19604@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: EC53180FD296 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Jun 04, 2020 at 09:51:10AM -0400, Zi Yan wrote: > On 4 Jun 2020, at 7:34, Matthew Wilcox wrote: > > On Thu, Jun 04, 2020 at 09:30:45AM +0530, Anshuman Khandual wrote: > >> +Quantifying Migration > >> +===================== > >> +Following events can be used to quantify page migration. > >> + > >> +- PGMIGRATE_SUCCESS > >> +- PGMIGRATE_FAIL > >> +- THP_MIGRATION_SUCCESS > >> +- THP_MIGRATION_FAILURE > >> + > >> +THP_MIGRATION_FAILURE in particular represents an event when a THP could not be > >> +migrated as a single entity following an allocation failure and ended up getting > >> +split into constituent normal pages before being retried. This event, along with > >> +PGMIGRATE_SUCCESS and PGMIGRATE_FAIL will help in quantifying and analyzing THP > >> +migration events including both success and failure cases. > > > > First, I'd suggest running this paragraph through 'fmt'. That way you > > don't have to care about line lengths. > > > > Second, this paragraph doesn't really explain what I need to know to > > understand the meaning of these numbers. When Linux attempts to migrate > > a THP, one of three things can happen: > > > > - It is migrated as a single THP > > - It is migrated, but had to be split > > - Migration fails > > > > How do I turn these four numbers into an understanding of how often each > > of those three situations happen? And why do we need four numbers to > > report three situations? > > > > Or is there something else that can happen? If so, I'd like that explained > > here too ;-) > > PGMIGRATE_SUCCESS and PGMIGRATE_FAIL record a combination of different events, > so it is not easy to interpret them. Let me try to explain them. Thanks! Very helpful explanation. > 1. migrating only base pages: PGMIGRATE_SUCCESS and PGMIGRATE_FAIL just mean > these base pages are migrated and fail to migrate respectively. > THP_MIGRATION_SUCCESS and THP_MIGRATION_FAILURE should be 0 in this case. > Simple. > > 2. migrating only THPs: > - PGMIGRATE_SUCCESS means THPs that are migrated and base pages > (from the split of THPs) that are migrated, > > - PGMIGRATE_FAIL means THPs that fail to migrate and base pages that fail to migrated. > > - THP_MIGRATION_SUCCESS means THPs that are migrated. > > - THP_MIGRATION_FAILURE means THPs that are split. > > So PGMIGRATE_SUCCESS - THP_MIGRATION_SUCCESS means the number of migrated base pages, > which are from the split of THPs. Are you sure about that? If I split a THP and each of those subpages migrates, won't I then see PGMIGRATE_SUCCESS increase by 512? > When it comes to analyze failed migration, PGMIGRATE_FAIL - THP_MIGRATION_FAILURE > means the number of pages that are failed to migrate, but we cannot tell how many > are base pages and how many are THPs. > > 3. migrating base pages and THP: > > The math should be very similar to the second case, except that > a) from PGMIGRATE_SUCCESS - THP_MIGRATION_SUCCESS, we cannot tell how many are pages begin > as base pages and how many are pages begin as THPs but become base pages after split; > b) from PGMIGRATE_FAIL - THP_MIGRATION_FAILURE, an additional case, > base pages that begin as base pages fail to migrate, is mixed into the number and we > cannot tell three cases apart. So why don't we just expose PGMIGRATE_SPLIT? That would be defined as the number of times we succeeded in migrating a THP but had to split it to succeed.