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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D8930C433EF for ; Wed, 10 Nov 2021 08:30:11 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 8CC7D610A3 for ; Wed, 10 Nov 2021 08:30:11 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 8CC7D610A3 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id 346A56B0071; Wed, 10 Nov 2021 03:30:11 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 2CDBC6B0072; Wed, 10 Nov 2021 03:30:11 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 16E176B0073; Wed, 10 Nov 2021 03:30:11 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0021.hostedemail.com [216.40.44.21]) by kanga.kvack.org (Postfix) with ESMTP id 0584C6B0071 for ; Wed, 10 Nov 2021 03:30:11 -0500 (EST) Received: from smtpin17.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id F233C824C439 for ; Wed, 10 Nov 2021 08:30:09 +0000 (UTC) X-FDA: 78792348180.17.C51408C Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by imf01.hostedemail.com (Postfix) with ESMTP id C030D509555E for ; Wed, 10 Nov 2021 08:29:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1636533009; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=zc9KdahAguXkghVeJqdY3150Du1QUqNhK9U4RYp1RCU=; b=HUp5dSG7adgN3Af7MLPs7T8lCAA+mDmCj3lFX3IjjIqyUSYj2Kq9P0OD0r7ydjmOZdzeR2 UFcAFvKQghc1g8xBNX1CDNLCrckYWauTfUW9Z4k92aTxm2ZBHuegoQI8TUYwiXfPH4bT+E JnKXgCV8YDMjVEGz9TTfETqLgCg4lCk= Received: from mail-pg1-f199.google.com (mail-pg1-f199.google.com [209.85.215.199]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-329-kaG4y54gMD2M45zGs7Qhxg-1; Wed, 10 Nov 2021 03:30:07 -0500 X-MC-Unique: kaG4y54gMD2M45zGs7Qhxg-1 Received: by mail-pg1-f199.google.com with SMTP id f7-20020a63f107000000b002db96febb74so1157698pgi.7 for ; Wed, 10 Nov 2021 00:30:07 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=zc9KdahAguXkghVeJqdY3150Du1QUqNhK9U4RYp1RCU=; b=ObhpRCgaI+dUVGBjMw3unyczAx1ogS4yfiQLD7okYZEtPDOZHSWpn79HuDfOjzBDkm +wE5qylFiH++drbbm3LfZN+qwCjNe71B2x6Ou2oUMazGLR+syFMFVCrh1Va2ODtN6Bhf lmLQzmvo5balzQjkk3pLTMtcSyeK15vnZ8HE5CXXFZuin2Nzeq3A0fXal5bWWuRdDn44 qxVJq8r7pqBC9PgS3N5rEi5yA9Fs5iXvMBTTLrEkn8A6Hxk+sq1wvKl4JtJEkFQBma3f FHrbN/UzOz0yx7gtmn6uUoWleVcaepx7meYhlys368mxYXTteD2QQD/1IXsROwrC+fd7 pGTQ== X-Gm-Message-State: AOAM531AM7p0sHYqLAW8IEdm0jY+xBshWPaDlzyWzZYKVgMhCTylp9Nc MKFqqrttuNwJL8FJWcKxZ43JP/LwOXtc7QslbjnoAxIsn8cWgvgFDavwb35neaK/SsL1wY6wFy4 10h3kCGw7VP0= X-Received: by 2002:a05:6a00:234f:b0:3eb:3ffd:6da2 with SMTP id j15-20020a056a00234f00b003eb3ffd6da2mr14429772pfj.15.1636533006778; Wed, 10 Nov 2021 00:30:06 -0800 (PST) X-Google-Smtp-Source: ABdhPJz5G/zio2lUCBLScLXJPHr7YuBo+SEEpRo7ak25/Vhyewmy2QoxXzy6zMkmUgeA4ABnG5roEw== X-Received: by 2002:a05:6a00:234f:b0:3eb:3ffd:6da2 with SMTP id j15-20020a056a00234f00b003eb3ffd6da2mr14429751pfj.15.1636533006522; Wed, 10 Nov 2021 00:30:06 -0800 (PST) Received: from localhost.localdomain ([94.177.118.35]) by smtp.gmail.com with ESMTPSA id s7sm23709986pfu.139.2021.11.10.00.30.01 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Wed, 10 Nov 2021 00:30:06 -0800 (PST) From: Peter Xu To: linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: peterx@redhat.com, Andrew Morton , Yang Shi , Hugh Dickins , David Hildenbrand , Alistair Popple , Andrea Arcangeli , Vlastimil Babka , "Kirill A . Shutemov" Subject: [PATCH RFC 1/2] mm: Don't skip swap entry even if zap_details specified Date: Wed, 10 Nov 2021 16:29:51 +0800 Message-Id: <20211110082952.19266-2-peterx@redhat.com> X-Mailer: git-send-email 2.32.0 In-Reply-To: <20211110082952.19266-1-peterx@redhat.com> References: <20211110082952.19266-1-peterx@redhat.com> MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="US-ASCII" X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: C030D509555E X-Stat-Signature: acssyfypq45wzgzqsnr7tc3su4ob4x1a Authentication-Results: imf01.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=HUp5dSG7; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf01.hostedemail.com: domain of peterx@redhat.com has no SPF policy when checking 170.10.129.124) smtp.mailfrom=peterx@redhat.com X-HE-Tag: 1636532995-896535 Content-Transfer-Encoding: quoted-printable 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: This check existed since the 1st git commit of Linux repository, but at t= hat time there's no page migration yet so I think it's okay. With page migration enabled, it should logically be possible that we zap = some shmem pages during migration. When that happens, IIUC the old code could= have the RSS counter accounted wrong on MM_SHMEMPAGES because we will zap the = ptes without decreasing the counters for the migrating entries. I have no uni= t test to prove it as I don't know an easy way to trigger this condition, though= . Besides, the optimization itself is already confusing IMHO to me in a few= points: - The wording "skip swap entries" is confusing, because we're not skipp= ing all swap entries - we handle device private/exclusive pages before that. - The skip behavior is enabled as long as zap_details pointer passed ov= er. It's very hard to figure that out for a new zap caller because it's u= nclear why we should skip swap entries when we have zap_details specified. - With modern systems, especially performance critical use cases, swap entries should be rare, so I doubt the usefulness of this optimizatio= n since it should be on a slow path anyway. - It is not aligned with what we do with huge pmd swap entries, where i= n zap_huge_pmd() we'll do the accounting unconditionally. This patch drops that trick, so we handle swap ptes coherently. Meanwhil= e we should do the same mapping check upon migration entries too. Signed-off-by: Peter Xu --- mm/memory.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) diff --git a/mm/memory.c b/mm/memory.c index 8f1de811a1dc..e454f3c6aeb9 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1382,16 +1382,14 @@ static unsigned long zap_pte_range(struct mmu_gat= her *tlb, continue; } =20 - /* If details->check_mapping, we leave swap entries. */ - if (unlikely(details)) - continue; - if (!non_swap_entry(entry)) rss[MM_SWAPENTS]--; else if (is_migration_entry(entry)) { struct page *page; =20 page =3D pfn_swap_entry_to_page(entry); + if (unlikely(zap_skip_check_mapping(details, page))) + continue; rss[mm_counter(page)]--; } if (unlikely(!free_swap_and_cache(entry))) --=20 2.32.0