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, FSL_HELO_FAKE,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 ACF35C4CEC5 for ; Thu, 12 Sep 2019 17:14:06 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 68B36206A5 for ; Thu, 12 Sep 2019 17:14:06 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="e9bGHgQC" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 68B36206A5 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 11CC96B0003; Thu, 12 Sep 2019 13:14:06 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 0CDDF6B0006; Thu, 12 Sep 2019 13:14:06 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id ED6556B0007; Thu, 12 Sep 2019 13:14:05 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0151.hostedemail.com [216.40.44.151]) by kanga.kvack.org (Postfix) with ESMTP id C65E56B0003 for ; Thu, 12 Sep 2019 13:14:05 -0400 (EDT) Received: from smtpin20.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with SMTP id 6A1D6824CA39 for ; Thu, 12 Sep 2019 17:14:05 +0000 (UTC) X-FDA: 75926916450.20.alarm05_40be90487c431 X-HE-Tag: alarm05_40be90487c431 X-Filterd-Recvd-Size: 4180 Received: from mail-pg1-f196.google.com (mail-pg1-f196.google.com [209.85.215.196]) by imf35.hostedemail.com (Postfix) with ESMTP for ; Thu, 12 Sep 2019 17:14:04 +0000 (UTC) Received: by mail-pg1-f196.google.com with SMTP id u17so13806120pgi.6 for ; Thu, 12 Sep 2019 10:14:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=FayExANUP9ViuhmtK38JGVU4eZPGVpUKAMO8IOFz2K0=; b=e9bGHgQCszlUto/KbmGaO4oNWaXNGlSe6GE4SRluwUF8dVEW5DMzGFqipp0/WinPBh t9cBCJWVuO2gSgD/77JynmL1upu84BvMO16sJCgNAe5iMtAo+xpNCfNEtAQk9rmbcrLM lz/6fdY4iRiUqUyIueMVEh+MLB7AjRnLa3Wu+IgzaicRj4r26JDj9tPRoPBjWm7oCDgC 0cU6ZEAkLuNJVA4lZEgRyGkwjutephLVRRK1hpMa3yLVM4Mdw0UhP+04M+AVJmE8mAcs 6IcMFXH0N8oAGLJnh4KyN/o2mJA+C+Qou7+XEg1a/YQrQIqJKKvQb79PCdlEx7Z9gtLx J2Fw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :references:mime-version:content-disposition:in-reply-to:user-agent; bh=FayExANUP9ViuhmtK38JGVU4eZPGVpUKAMO8IOFz2K0=; b=QFZCY9+qtIA/HjuK6dGvE3Aqq7iTTMHjgLdA0+Zz5lnYDkg5ZeGjANon6y0ZfhLEOI j48TAt3SQwzDVRCNXt3siWjSNuhNAnzImV3+nsA/Sxy3h65EFphqgWysdQiPspDMsAZM v3it9GVXS9pLTx2hN+kue63EorBKfOyJ3gXns0HrRmB7QmAJYrFbNnj4vDUX7jy/MN34 1iwuVwqthaYfevjO8dseBBIdBehGk7Mbd8jGpuE8nA3HUxd3xScYvmZrNqFY5X4/44Da 2Pkm7myF03DTCTSnEG+77qsd7eZhmSUdtNqMjOmjZU6BQ/Hwczy5N0uuT/z80Uly8O0K e0VQ== X-Gm-Message-State: APjAAAXA6xvG3sAUfy5ikSj/UxTKLbMWPQwx9zRcuDOYznTKb3e0R/gY QB+Thz1fqZnPi75xctLj3mE= X-Google-Smtp-Source: APXvYqzMJFI9O5++NJ1Dr/5RymJQJdpHX78RprFF+Eln41evdXBfAlFauX7if8pCw84GvaZsJbjbGA== X-Received: by 2002:a63:195f:: with SMTP id 31mr39719349pgz.225.1568308443521; Thu, 12 Sep 2019 10:14:03 -0700 (PDT) Received: from google.com ([2620:15c:211:1:3e01:2939:5992:52da]) by smtp.gmail.com with ESMTPSA id z14sm4825667pgj.22.2019.09.12.10.14.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 12 Sep 2019 10:14:01 -0700 (PDT) Date: Thu, 12 Sep 2019 10:14:00 -0700 From: Minchan Kim To: Vinayak Menon Cc: linux-mm@kvack.org Subject: Re: [PATCH] mm: fix the race between swapin_readahead and SWP_SYNCHRONOUS_IO path Message-ID: <20190912171400.GA119788@google.com> References: <1567169011-4748-1-git-send-email-vinmenon@codeaurora.org> <20190909232613.GA39783@google.com> <9df3bb51-2094-c849-8171-dce6784e1e70@codeaurora.org> <20190910175116.GB39783@google.com> 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-Bogosity: Ham, tests=bogofilter, spamicity=0.002111, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Hi Vinayak, On Wed, Sep 11, 2019 at 03:37:23PM +0530, Vinayak Menon wrote: < snip > > >> Can swapcache check be done like below, before taking the SWP_SYNCHRONOUS_IO path, as an alternative ? > > With your approach, what prevent below scenario? > > > > A B > > > > do_swap_page > > SWP_SYNCHRONOUS_IO && __swap_count == 1 > > > As shrink_page_list is picking the page from LRU and B is trying to read from swap simultaneously, I assume someone had read > > the page from swap prior to B, when its swap_count was say 2 (for it to be reclaimed by shrink_page_list now) It could happen after B saw __swap_count == 1. Think about forking new process. In that case, swap_count is 2 and the forked process will access the page(it ends up freeing zram slot but the page would be swap cache. However, B process doesn't know it).