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=-0.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 8814DC433E0 for ; Wed, 13 May 2020 21:15:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 782CC20675 for ; Wed, 13 May 2020 21:15:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589404522; bh=Ea3KACcclZ07aASwPFWht/xTSHvjT8unfYTdZBQH6q4=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=TLPYSeOITbRonaZ9yUGTD1Ud3Ia48K+kQUFc1ahNG54B5abaQu8IujMmVeXJrvsnj d4yqw2Xu5wO26ewPQCuQeYh2R8Aq20JbvHQSicBfnEYHpIkT0sZJCDz78yZ95duyIv vSbOMiW1DeVglzHtsEUoQoGcQvNT5UewLpPiEbAs= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728567AbgEMVPV (ORCPT ); Wed, 13 May 2020 17:15:21 -0400 Received: from mail.kernel.org ([198.145.29.99]:35576 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727063AbgEMVPV (ORCPT ); Wed, 13 May 2020 17:15:21 -0400 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 0267920575; Wed, 13 May 2020 21:15:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589404520; bh=Ea3KACcclZ07aASwPFWht/xTSHvjT8unfYTdZBQH6q4=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=uEmayH51kFnINlCgnG8z6jlPjUkPsWCZjVK5iGMheGtLdiu9OLUjClWIf8Hhjn6V9 bDEocbRLdn2kXTkQUYHQXy9GvXyiJCh8d2mtV7zTmENXvZJVLWE/GM2UTqUul2Zk+c G0HTOCKlIApdY4I6jo/LZaRhTeNRf+pQFy13cUOs= Date: Wed, 13 May 2020 14:15:19 -0700 From: Andrew Morton To: Johannes Weiner Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Dave Chinner , Yafang Shao , Michal Hocko , Roman Gushchin , Linus Torvalds , Al Viro , kernel-team@fb.com Subject: Re: [PATCH] vfs: keep inodes with page cache off the inode shrinker LRU Message-Id: <20200513141519.061f8fca4788cd02b4d7068f@linux-foundation.org> In-Reply-To: <20200512212936.GA450429@cmpxchg.org> References: <20200211175507.178100-1-hannes@cmpxchg.org> <20200512212936.GA450429@cmpxchg.org> 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 Tue, 12 May 2020 17:29:36 -0400 Johannes Weiner wrote: > > ... > > Solution > > This patch fixes the aging inversion described above on > !CONFIG_HIGHMEM systems, without reintroducing the problems associated > with excessive shrinker LRU rotations, by keeping populated inodes off > the shrinker LRUs entirely. > > Currently, inodes are kept off the shrinker LRU as long as they have > an elevated i_count, indicating an active user. Unfortunately, the > page cache cannot simply hold an i_count reference, because unlink() > *should* result in the inode being dropped and its cache invalidated. > > Instead, this patch makes iput_final() consult the state of the page > cache and punt the LRU linking to the VM if the inode is still > populated; the VM in turn checks the inode state when it depopulates > the page cache, and adds the inode to the LRU if necessary. > > This is not unlike what we do for dirty inodes, which are moved off > the LRU permanently until writeback completion puts them back on (iff > still unused). We can reuse the same code -- inode_add_lru() - here. > > This is also not unlike page reclaim, where the lower VM layer has to > negotiate state with the higher VFS layer. Follow existing precedence > and handle the inversion as much as possible on the VM side: > > - introduce an I_PAGES flag that the VM maintains under the i_lock, so > that any inode code holding that lock can check the page cache state > without having to lock and inspect the struct address_space Maintaining the same info in two places is a hassle. Is this optimization worthwhile? > - introduce inode_pages_set() and inode_pages_clear() to maintain the > inode LRU state from the VM side, then update all cache mutators to > use them when populating the first cache entry or clearing the last > > With this, the concept of "inodesteal" - where the inode shrinker > drops page cache - is relegated to CONFIG_HIGHMEM systems only. The VM > is in charge of the cache, the shrinker in charge of struct inode. How tested is this on highmem machines? > Footnotes > > - For debuggability, add vmstat counters that track the number of > times a new cache entry pulls a previously unused inode off the LRU > (pginoderescue), as well as how many times existing cache deferred > an LRU addition. Keep the pginodesteal/kswapd_inodesteal counters > for backwards compatibility, but they'll just show 0 now. > > - Fix /proc/sys/vm/drop_caches to drop shadow entries from the page > cache. Not doing so has always been a bit strange, but since most > people drop cache and metadata cache together, the inode shrinker > would have taken care of them before - no more, so do it VM-side. > > ... > > 14 files changed, 208 insertions(+), 34 deletions(-) Patch is surprisingly large.