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=-0.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 16884C3F68F for ; Tue, 11 Feb 2020 16:34:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E3F1E20873 for ; Tue, 11 Feb 2020 16:34:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581438851; bh=HAF9UF+4lnB297TrbRVoBXSSejhgiWznackbBSrtY70=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=GkppuwkG2afmlNa7h2BrE3p02kSZDMgK+i1JIbGpfGtLcmj/UcDYJY/WZRugPUYle RliS7j1ouKP0DjRXzRdDYaBMhKaYImtAWN/pGFMgWxBIprWAImjp/OU43XUG3vBp1+ ZZ1JPxc3VVxUePGflqd52ROjAEeWCA9iHgyfFADg= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730849AbgBKQeK (ORCPT ); Tue, 11 Feb 2020 11:34:10 -0500 Received: from mail-pf1-f193.google.com ([209.85.210.193]:46523 "EHLO mail-pf1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728295AbgBKQeJ (ORCPT ); Tue, 11 Feb 2020 11:34:09 -0500 Received: by mail-pf1-f193.google.com with SMTP id k29so5715655pfp.13 for ; Tue, 11 Feb 2020 08:34:08 -0800 (PST) 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=DcogQqT/L9uwP1yMzCrGQYpSSLcJ6csEli1u/M+9NC4=; b=LRxzWKOC4zHMz/9PTrk1682dTwlx4tFC6jZmyDfZA4fhdNbthovhVHVqMZ1qmaKiip 71flcMUrOJ6szRSPZgJB9Ir2AT/lQJWsflPMrdiDSRd9BvtguFv2ZKzJhOptvfSKCsoR EpCXoei53H5m+CTK40OenXUgOX0bnAUGcB4Sse1fP7ZjjQ23i3/Hy9cqgTPtV4Q5J1bK YS8phOfP8spleZNSTbvtUbjd7Mv+z8CleeYMbOdYvRfhsKGhk5vnrW6RlNZUmiIh1o5J NFOstpWhwRB8OZ7h+cTk5w+rwqX0pKd9RUtawYBOzTN2nRuwwCGp7aD9DCoPU5OIAB6R TFow== 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=DcogQqT/L9uwP1yMzCrGQYpSSLcJ6csEli1u/M+9NC4=; b=uQV8M/S8ncduDrWoBJ0RKNK1MfHgFxbrQzg27a0D0E3qWovyvmDCTV42km2nD2WQ4A 6D9XI1idPX2X4UZzLeNocezLz72UChuks04muRokkppXgFD7nfC+UsDZvr2t8x+gF9SK pTZ+4oC1QCO3jXS0IIh5jg/cSKPJWq+DX5RHsmhqGpd1DtirHvGr2P1GyueyA2DwqXT3 yU8vxeD6gkihCGWSwZFenxbd7QPia67T3Ex2Kf563ljAiJkNXQcZiYSsWDyDwcdm6r9j qBL52XL5xmzvm4wy1Q/TBc3YiYG5EOU1eSmzNq+ZvxFanaD/h5t4lg9WPn/JNpKenT5w TzWw== X-Gm-Message-State: APjAAAWXg/LocT9WSjsZKHED84DNVdweEgxrTHXmDVtYaHSyYYKsdxlz xwylXWP8duZwmQyx0dv4CiE= X-Google-Smtp-Source: APXvYqyuoIukPc1izp+pVUfL075f0kUmc4wnvEqg2lvp7wpaD4YxIQBjABu+TnwOdTvlhfsL5K33qw== X-Received: by 2002:a63:4c4:: with SMTP id 187mr7719262pge.362.1581438847389; Tue, 11 Feb 2020 08:34:07 -0800 (PST) Received: from google.com ([2620:15c:211:1:3e01:2939:5992:52da]) by smtp.gmail.com with ESMTPSA id ep2sm3831545pjb.31.2020.02.11.08.34.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 11 Feb 2020 08:34:06 -0800 (PST) Date: Tue, 11 Feb 2020 08:34:04 -0800 From: Minchan Kim To: Matthew Wilcox Cc: Andrew Morton , linux-mm , Josef Bacik , Johannes Weiner , Jan Kara , LKML Subject: Re: [PATCH] mm: fix long time stall from mm_populate Message-ID: <20200211163404.GC242563@google.com> References: <20200211001958.170261-1-minchan@kernel.org> <20200211011021.GP8731@bombadil.infradead.org> <20200211035004.GA242563@google.com> <20200211035412.GR8731@bombadil.infradead.org> <20200211042536.GB242563@google.com> <20200211122323.GS8731@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200211122323.GS8731@bombadil.infradead.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 11, 2020 at 04:23:23AM -0800, Matthew Wilcox wrote: > On Mon, Feb 10, 2020 at 08:25:36PM -0800, Minchan Kim wrote: > > On Mon, Feb 10, 2020 at 07:54:12PM -0800, Matthew Wilcox wrote: > > > On Mon, Feb 10, 2020 at 07:50:04PM -0800, Minchan Kim wrote: > > > > On Mon, Feb 10, 2020 at 05:10:21PM -0800, Matthew Wilcox wrote: > > > > > On Mon, Feb 10, 2020 at 04:19:58PM -0800, Minchan Kim wrote: > > > > > > filemap_fault > > > > > > find a page form page(PG_uptodate|PG_readahead|PG_writeback) > > > > > > > > > > Uh ... That shouldn't be possible. > > > > > > > > Please see shrink_page_list. Vmscan uses PG_reclaim to accelerate > > > > page reclaim when the writeback is done so the page will have both > > > > flags at the same time and the PG reclaim could be regarded as > > > > PG_readahead in fault conext. > > > > > > What part of fault context can make that mistake? The snippet I quoted > > > below is from page_cache_async_readahead() where it will clearly not > > > make that mistake. There's a lot of code here; please don't presume I > > > know all the areas you're talking about. > > > > Sorry about being not clear. I am saying filemap_fault -> > > do_async_mmap_readahead > > > > Let's assume the page is hit in page cache and vmf->flags is !FAULT_FLAG > > TRIED so it calls do_async_mmap_readahead. Since the page has PG_reclaim > > and PG_writeback by shrink_page_list, it goes to > > > > do_async_mmap_readahead > > if (PageReadahead(page)) > > fpin = maybe_unlock_mmap_for_io(); > > page_cache_async_readahead > > if (PageWriteback(page)) > > return; > > ClearPageReadahead(page); <- doesn't reach here until the writeback is clear > > > > So, mm_populate will repeat the loop until the writeback is done. > > It's my just theory but didn't comfirm it by the testing. > > If I miss something clear, let me know it. > > Ah! Surely the right way to fix this is ... I'm not sure it's right fix. Actually, I wanted to remove PageWriteback check in page_cache_async_readahead because I don't see corelation. Why couldn't we do readahead if the marker page is PG_readahead|PG_writeback design PoV? Only reason I can think of is it makes *a page* will be delayed for freeing since we removed PG_reclaim bit, which would be over-optimization for me. Other concern is isn't it's racy? IOW, page was !PG_writeback at the check below in your snippet but it was under PG_writeback in page_cache_async_readahead and then the IO was done before refault reaching the code again. It could be repeated *theoretically* even though it's very hard to happen in real practice. Thus, I think it would be better to remove PageWriteback check from page_cache_async_readahead if we really want to go the approach. However, page_cache_async_readahead has another condition to bail out: ra_pages I think it's also racy with fadvise or shrinking the window size from other tasks. That's why I thought second trial with non-fault retry logic from caller would fix all potnetial issues all at once like page fault handler have done. > > +++ b/mm/filemap.c > @@ -2420,7 +2420,7 @@ static struct file *do_async_mmap_readahead(struct vm_fault *vmf, > return fpin; > if (ra->mmap_miss > 0) > ra->mmap_miss--; > - if (PageReadahead(page)) { > + if (!PageWriteback(page) && PageReadahead(page)) { > fpin = maybe_unlock_mmap_for_io(vmf, fpin); > page_cache_async_readahead(mapping, ra, file, > page, offset, ra->ra_pages); >