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=-11.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=unavailable 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 7A7B2C433DF for ; Wed, 12 Aug 2020 05:40:48 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 238B820771 for ; Wed, 12 Aug 2020 05:40:47 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="CAHggqIK" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 238B820771 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 625E18D0001; Wed, 12 Aug 2020 01:40:47 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 5D7036B000D; Wed, 12 Aug 2020 01:40:47 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4C6428D0001; Wed, 12 Aug 2020 01:40:47 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0160.hostedemail.com [216.40.44.160]) by kanga.kvack.org (Postfix) with ESMTP id 345A06B000C for ; Wed, 12 Aug 2020 01:40:47 -0400 (EDT) Received: from smtpin29.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id CF5F8181AEF15 for ; Wed, 12 Aug 2020 05:40:46 +0000 (UTC) X-FDA: 77140817292.29.shoe90_030b27c26fe9 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin29.hostedemail.com (Postfix) with ESMTP id 9E4B318086CD2 for ; Wed, 12 Aug 2020 05:40:46 +0000 (UTC) X-HE-Tag: shoe90_030b27c26fe9 X-Filterd-Recvd-Size: 4865 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [63.128.21.124]) by imf20.hostedemail.com (Postfix) with ESMTP for ; Wed, 12 Aug 2020 05:40:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1597210845; 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: in-reply-to:in-reply-to:references:references; bh=YjQCImwrKKAQU3JlwtdjkqTIDAo/dvR77KpYtYakGUs=; b=CAHggqIKh5hl0R9thX/hUuskKoWaV6Vq1R/FCmiFSUsQS0nwynEQj8GT4pfGLb6uA3d0hf ZC4CYD5o/sCqNtGXH5WX3aSJ/6Szz+LYht3puoxQtjSxNR2k3/1TO8qb7YJqcLsKxO7u0f j1ipNXHTWOMG0n+GsWcIGTY/w+wSAMo= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-498-ejtbnAT5P5yGMymPcfsSEg-1; Wed, 12 Aug 2020 01:40:41 -0400 X-MC-Unique: ejtbnAT5P5yGMymPcfsSEg-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 302A61005504; Wed, 12 Aug 2020 05:40:40 +0000 (UTC) Received: from localhost (ovpn-12-45.pek2.redhat.com [10.72.12.45]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 377D360C84; Wed, 12 Aug 2020 05:40:37 +0000 (UTC) Date: Wed, 12 Aug 2020 13:40:35 +0800 From: Baoquan He To: Mike Kravetz Cc: Michal Hocko , Wei Yang , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 10/10] mm/hugetlb: not necessary to abuse temporary page to workaround the nasty free_huge_page Message-ID: <20200812054035.GD10792@MiWiFi-R3L-srv> References: <20200807091251.12129-1-richard.weiyang@linux.alibaba.com> <20200807091251.12129-11-richard.weiyang@linux.alibaba.com> <20200810021737.GV14854@MiWiFi-R3L-srv> <129cc03e-c6d5-24f8-2f3c-f5a3cc821e76@oracle.com> <20200811015148.GA10792@MiWiFi-R3L-srv> <20200811065406.GC4793@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Rspamd-Queue-Id: 9E4B318086CD2 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 08/11/20 at 02:43pm, Mike Kravetz wrote: > Here is a patch to do that. However, we are optimizing a return path in > a race condition that we are unlikely to ever hit. I 'tested' it by allocating > an 'extra' page and freeing it via this method in alloc_surplus_huge_page. > > From 864c5f8ef4900c95ca3f6f2363a85f3cb25e793e Mon Sep 17 00:00:00 2001 > From: Mike Kravetz > Date: Tue, 11 Aug 2020 12:45:41 -0700 > Subject: [PATCH] hugetlb: optimize race error return in > alloc_surplus_huge_page > > The routine alloc_surplus_huge_page() could race with with a pool > size change. If this happens, the allocated page may not be needed. > To free the page, the current code will 'Abuse temporary page to > workaround the nasty free_huge_page codeflow'. Instead, directly > call the low level routine that free_huge_page uses. This works > out well because the page is new, we hold the only reference and > already hold the hugetlb_lock. > > Signed-off-by: Mike Kravetz > --- > mm/hugetlb.c | 13 ++++++++----- > 1 file changed, 8 insertions(+), 5 deletions(-) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index 590111ea6975..ac89b91fba86 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -1923,14 +1923,17 @@ static struct page *alloc_surplus_huge_page(struct hstate *h, gfp_t gfp_mask, > /* > * We could have raced with the pool size change. > * Double check that and simply deallocate the new page > - * if we would end up overcommiting the surpluses. Abuse > - * temporary page to workaround the nasty free_huge_page > - * codeflow > + * if we would end up overcommiting the surpluses. > */ > if (h->surplus_huge_pages >= h->nr_overcommit_huge_pages) { > - SetPageHugeTemporary(page); > + /* > + * Since this page is new, we hold the only reference, and > + * we already hold the hugetlb_lock call the low level free > + * page routine. This saves at least a lock roundtrip. > + */ > + (void)put_page_testzero(page); /* don't call destructor */ > + update_and_free_page(h, page); Yeah, taking this code change, or keeping the temporary page way as is, both looks good. > spin_unlock(&hugetlb_lock); > - put_page(page); > return NULL; > } else { > h->surplus_huge_pages++;