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,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 735A3C3F68F for ; Thu, 13 Feb 2020 02:00:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4289B21739 for ; Thu, 13 Feb 2020 02:00:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581559234; bh=1SwzLLEyuLUC0YcReqmRfMKXlXhD3aV8WxBnviIaFfw=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=mdj2te9FM6FSVFADXuc0URcgCNdSd96c3TooTjZeQWxh1RPFF1zO7+vS9+QieqvKJ B3QceEXXiSwT7wdCcMvpsQ+uZlVTlP+zGT4rP11f/9s7tD6r3OJfWDRrvJ9stnIw2F aR+EMoasBBME3S5w8ythdKOSzraXHZGTY9Ccar/A= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729394AbgBMCAd (ORCPT ); Wed, 12 Feb 2020 21:00:33 -0500 Received: from mail.kernel.org ([198.145.29.99]:56510 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729289AbgBMCAd (ORCPT ); Wed, 12 Feb 2020 21:00:33 -0500 Received: from localhost.localdomain (c-73-231-172-41.hsd1.ca.comcast.net [73.231.172.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 7F6D220659; Thu, 13 Feb 2020 02:00:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581559231; bh=1SwzLLEyuLUC0YcReqmRfMKXlXhD3aV8WxBnviIaFfw=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=Ji9FsdzXaPsvVFPj+2xKMPRNsik5cVbQqgjM0tqJzbEPtUxtKWB6/YouFDGKbnSnB U2Va2Xn6MjTKeCaGxqfCT9iOOZq5kE8Fj30hFCyyND00SKiKNzpq40WquOzTfYBXn5 uFxCx+xit6Vc0I+VmJzv1HtXyJpVsIC2KqXvLuoU= Date: Wed, 12 Feb 2020 18:00:30 -0800 From: Andrew Morton To: Minchan Kim Cc: Matthew Wilcox , Jan Kara , linux-mm , Josef Bacik , Johannes Weiner , LKML Subject: Re: [PATCH] mm: fix long time stall from mm_populate Message-Id: <20200212180030.a89da9c4cf2b9d11efcc25db@linux-foundation.org> In-Reply-To: <20200212231210.GA233109@google.com> References: <20200211042536.GB242563@google.com> <20200211122323.GS8731@bombadil.infradead.org> <20200211163404.GC242563@google.com> <20200211172803.GA7778@bombadil.infradead.org> <20200211175731.GA185752@google.com> <20200212101804.GD25573@quack2.suse.cz> <20200212174015.GB93795@google.com> <20200212182851.GG7778@bombadil.infradead.org> <20200212195322.GA83146@google.com> <20200212142435.0b7e938fe8112fa35fcbcc71@linux-foundation.org> <20200212231210.GA233109@google.com> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 12 Feb 2020 15:12:10 -0800 Minchan Kim wrote: > On Wed, Feb 12, 2020 at 02:24:35PM -0800, Andrew Morton wrote: > > On Wed, 12 Feb 2020 11:53:22 -0800 Minchan Kim wrote: > > > > > > That's definitely wrong. It'll clear PageReclaim and then pretend it did > > > > nothing wrong. > > > > > > > > return !PageWriteback(page) || > > > > test_and_clear_bit(PG_reclaim, &page->flags); > > > > > > > > > > Much better, Thanks for the review, Matthew! > > > If there is no objection, I will send two patches to Andrew. > > > One is PageReadahead strict, the other is limit retry from mm_populate. > > > > With much more detailed changelogs, please! > > > > This all seems rather screwy. if a page is under writeback then it is > > uptodate and we should be able to fault it in immediately. > > Hi Andrew, > > This description in cover-letter will work? If so, I will add each part > below in each patch. > > Subject: [PATCH 0/3] fixing mm_populate long stall > > I got several reports major page fault takes several seconds sometime. > When I review drop mmap_sem in page fault hanlder, I found several bugs. > > CPU 1 CPU 2 > mm_populate > for () > .. > ret = populate_vma_page_range > __get_user_pages > faultin_page > handle_mm_fault > filemap_fault > do_async_mmap_readahead > shrink_page_list > pageout > SetPageReclaim(=SetPageReadahead) > writepage > SetPageWriteback > if (PageReadahead(page)) > maybe_unlock_mmap_for_io > up_read(mmap_sem) > page_cache_async_readahead() > if (PageWriteback(page)) > return; > > here, since ret from populate_vma_page_range is zero, > the loop continue to run with same address with previous > iteration. It will repeat the loop until the page's > writeout is done(ie, PG_writeback or PG_reclaim clear). The populate_vma_page_range() kerneldoc is wrong. "return 0 on success, negative error code on error". Care to fix that please? > We could fix the above specific case via adding PageWriteback. IOW, > > ret = populate_vma_page_range > ... > ... > filemap_fault > do_async_mmap_readahead > if (!PageWriteback(page) && PageReadahead(page)) > maybe_unlock_mmap_for_io > up_read(mmap_sem) > page_cache_async_readahead() > if (PageWriteback(page)) > return; Well yes, but the testing of PageWriteback() is a hack added in fe3cba17c49471 to permit the sharing of PG_reclaim and PG_readahead. If we didn't need that hack then we could avoid adding new hacks to hack around the old hack :(. Have you considered anything along those lines? Rework how we handle PG_reclaim/PG_readahead? > That's a thing [3/3] is fixing here. Even though it could fix the > problem effectively, it has still livelock problem theoretically > because the page of faulty address could be reclaimed and then > allocated/become readahead marker on other CPUs during faulty > process is retrying in mm_populate's loop. Really? filemap_fault()'s if (!lock_page_maybe_drop_mmap(vmf, page, &fpin)) goto out_retry; /* Did it get truncated? */ if (unlikely(compound_head(page)->mapping != mapping)) { unlock_page(page); put_page(page); goto retry_find; } should handle such cases? > [2/3] is fixing the > such livelock via limiting retry count. I wouldn't call that "fixing" :( > There is another hole for the livelock or hang of the process as well > as ageWriteback - ra_pages. > > mm_populate > for () > .. > ret = populate_vma_page_range > __get_user_pages > faultin_page > handle_mm_fault > filemap_fault > do_async_mmap_readahead > if (PageReadahead(page)) > maybe_unlock_mmap_for_io > up_read(mmap_sem) > page_cache_async_readahead() > if (!ra->ra_pages) > return; > > It will repeat the loop until ra->ra_pages become non-zero. > [1/3] is fixing the problem. >