Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757620Ab1FXNth (ORCPT ); Fri, 24 Jun 2011 09:49:37 -0400 Received: from mail.betterlinux.com ([199.58.199.50]:34135 "EHLO mail.betterlinux.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752174Ab1FXNtg (ORCPT ); Fri, 24 Jun 2011 09:49:36 -0400 From: Andrea Righi To: Andrew Morton Cc: Minchan Kim , Rik van Riel , Peter Zijlstra , Johannes Weiner , KAMEZAWA Hiroyuki , Andrea Arcangeli , Hugh Dickins , Jerry James , Marcus Sorensen , Matt Heaton , KOSAKI Motohiro , Theodore Tso , Shaohua Li , =?UTF-8?q?P=C3=A1draig=20Brady?= , linux-mm , LKML Subject: [PATCH v3 0/2] fadvise: support POSIX_FADV_NOREUSE Date: Fri, 24 Jun 2011 15:49:08 +0200 Message-Id: <1308923350-7932-1-git-send-email-andrea@betterlinux.com> X-Mailer: git-send-email 1.7.4.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3545 Lines: 85 There were some reported problems in the past about trashing page cache when a backup software (i.e., rsync) touches a huge amount of pages (see for example [1]). This problem has been almost fixed by the Minchan Kim's patch [2] and a proper use of fadvise() in the backup software. For example this patch set [3] has been proposed for inclusion in rsync. However, there can be still other similar trashing problems: when the backup software reads all the source files, some of them may be part of the actual working set of the system. When a POSIX_FADV_DONTNEED is performed _all_ pages are evicted from pagecache, both the working set and the use-once pages touched only by the backup software. A previous proposal [4] tried to resolve this problem being less agressive in invalidating active pages, moving them to the inactive list intead of just evict them from the page cache. However, this approach changed completely the old behavior of invalidate_mapping_pages(), that is not only used by fadvise. The new solution maps POSIX_FADV_NOREUSE to the less-agressive page invalidation policy. With POSIX_FADV_NOREUSE active pages are moved to the tail of the inactive list, and pages in the inactive list are just removed from page cache. Pages mapped by other processes or unevictable pages are not touched at all. In this way if the backup was the only user of a page, that page will be immediately removed from the page cache by calling POSIX_FADV_NOREUSE. If the page was also touched by other tasks it'll be moved to the inactive list, having another chance of being re-added to the working set, or simply reclaimed when memory is needed. In conclusion, now userspace applications that want to drop some page cache pages can choose between the following advices: POSIX_FADV_DONTNEED = drop page cache if possible POSIX_FADV_NOREUSE = reduce page cache eligibility Testcase: - create a 1GB file called "zero" - run md5sum zero to read all the pages in page cache (this is to simulate the user activity on this file) - run rsync zero zero_copy - re-run md5sum zero (user activity on the working set) and measure the time to complete this command rsync has been patched with [3], using POSIX_FADV_DONTNEED in one case and POSIX_FADV_NOREUSE in the other case. Results: - after the backup run: # perf stat -e block:block_bio_queue md5sum zero avg elapsed time block:block_bio_queue rsync-dontneed 4.24s 2,072 rsync-noreuse 2.22s 0 [1] http://marc.info/?l=rsync&m=128885034930933&w=2 [2] https://lkml.org/lkml/2011/2/20/57 [3] http://lists.samba.org/archive/rsync/2010-November/025827.html [4] https://lkml.org/lkml/2011/6/23/35 ChangeLog v2 -> v3: - do not change the old POSIX_FADV_DONTNEED behavior and implement the less aggressive page cache invalidation policy using POSIX_FADV_NOREUSE - fix comments in the code [PATCH v3 1/2] mm: introduce __invalidate_mapping_pages() [PATCH v3 2/2] fadvise: implement POSIX_FADV_NOREUSE include/linux/fs.h | 7 +++++-- mm/fadvise.c | 11 ++++++----- mm/swap.c | 2 +- mm/truncate.c | 40 ++++++++++++++++++++++++++++++---------- 4 files changed, 42 insertions(+), 18 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/