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=-5.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 119E1C433DF for ; Sat, 25 Jul 2020 10:14:57 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id C1EC4206D7 for ; Sat, 25 Jul 2020 10:14:56 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Y++mNFQ3" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C1EC4206D7 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 2D3896B0002; Sat, 25 Jul 2020 06:14:56 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 2837E6B0003; Sat, 25 Jul 2020 06:14:56 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 173806B0006; Sat, 25 Jul 2020 06:14:56 -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 F1BCA6B0002 for ; Sat, 25 Jul 2020 06:14:55 -0400 (EDT) Received: from smtpin11.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 48EDF8248047 for ; Sat, 25 Jul 2020 10:14:55 +0000 (UTC) X-FDA: 77076189750.11.van84_6117d8426f4f Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin11.hostedemail.com (Postfix) with ESMTP id 0CE80184600C8 for ; Sat, 25 Jul 2020 10:14:55 +0000 (UTC) X-HE-Tag: van84_6117d8426f4f X-Filterd-Recvd-Size: 4608 Received: from us-smtp-delivery-1.mimecast.com (us-smtp-1.mimecast.com [205.139.110.61]) by imf10.hostedemail.com (Postfix) with ESMTP for ; Sat, 25 Jul 2020 10:14:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1595672093; 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=b0AOSE86PGeB1I9Z9HMCGCB3b0fmc6DBmuHd8pPAROo=; b=Y++mNFQ3HrrYgRlxqSr5x4gYDeFBSX8pnpAxzpi/v/SQG884gBTS34yElOXTcrd1PC3Op1 UktxA6xzKyK/MazrAWkVMpn+U62+EM4qbBsbaDJ+Z6iGpUAWLtRe7YTLYEWWW8Lph9qKm1 ZR2jF3BXAXp2LMDmwAjiE0HI0Ve558c= 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-384-nScs2uXVMfyq-xnABE0aEg-1; Sat, 25 Jul 2020 06:14:51 -0400 X-MC-Unique: nScs2uXVMfyq-xnABE0aEg-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 289B91009600; Sat, 25 Jul 2020 10:14:50 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.40.192.25]) by smtp.corp.redhat.com (Postfix) with SMTP id C482270105; Sat, 25 Jul 2020 10:14:47 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Sat, 25 Jul 2020 12:14:49 +0200 (CEST) Date: Sat, 25 Jul 2020 12:14:46 +0200 From: Oleg Nesterov To: Linus Torvalds Cc: Hugh Dickins , Michal Hocko , Linux-MM , LKML , Andrew Morton , Tim Chen , Michal Hocko Subject: Re: [RFC PATCH] mm: silence soft lockups from unlock_page Message-ID: <20200725101445.GB3870@redhat.com> References: <20200723124749.GA7428@redhat.com> <20200724152424.GC17209@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Rspamd-Queue-Id: 0CE80184600C8 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam01 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 07/24, Linus Torvalds wrote: > > I just realized that one thing we could do is to not even test the > page bit for the shared case in the wakeup path. > > Because anybody who uses the non-exclusive "wait_on_page_locked()" or > "wait_on_page_writeback()" isn't actually interested in the bit state > any more at that point. All they care about is that somebody cleared > it - not whether it was then re-taken again. > > So instead of keeping them on the list - or stopping the waitqueue > walk because somebody else got the bit - we could just mark them > successfully done, wake them up, and remove those entries from the > list. Heh. I too thought about this. And just in case, your patch looks correct to me. But I can't really comment this behavioural change. Perhaps it should come in a separate patch? In essense, this partly reverts your commit 3510ca20ece0150 ("Minor page waitqueue cleanups"). I mean this part: (b) we don't want to put the non-locking waiters always on the front of the queue, and the locking waiters always on the back. Not only is that unfair, it means that we wake up thousands of reading threads that will just end up being blocked by the writer later anyway. ... @@ -972,10 +976,7 @@ static inline int wait_on_page_bit_common(wait_queue_head_t *q, spin_lock_irq(&q->lock); if (likely(list_empty(&wait->entry))) { - if (lock) - __add_wait_queue_entry_tail_exclusive(q, wait); - else - __add_wait_queue(q, wait); + __add_wait_queue_entry_tail(q, wait); SetPageWaiters(page); } Oleg.