From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH 12/12] bdi: use bdi_stat_sum() for more accurate debugfs stats Date: Wed, 18 Nov 2009 11:38:49 +0100 Message-ID: <1258540729.3918.211.camel@laptop> References: <20091118082648.140755818@intel.com> <20091118082846.921451469@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: Andrew Morton , linux-fsdevel@vger.kernel.org To: Wu Fengguang Return-path: Received: from casper.infradead.org ([85.118.1.10]:46848 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751890AbZKRKis (ORCPT ); Wed, 18 Nov 2009 05:38:48 -0500 In-Reply-To: <20091118082846.921451469@intel.com> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Wed, 2009-11-18 at 16:27 +0800, Wu Fengguang wrote: > plain text document attachment (bdi-debug-dump-sum.patch) > CC: Peter Zijlstra > Signed-off-by: Wu Fengguang > --- > mm/backing-dev.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > --- linux.orig/mm/backing-dev.c 2009-11-18 16:25:28.000000000 +0800 > +++ linux/mm/backing-dev.c 2009-11-18 16:26:10.000000000 +0800 > @@ -104,8 +104,8 @@ static int bdi_debug_stats_show(struct s > "wb_mask: %8lx\n" > "wb_list: %8u\n" > "wb_cnt: %8u\n", > - (unsigned long) K(bdi_stat(bdi, BDI_WRITEBACK)), > - (unsigned long) K(bdi_stat(bdi, BDI_RECLAIMABLE)), > + (unsigned long) K(bdi_stat_sum(bdi, BDI_WRITEBACK)), > + (unsigned long) K(bdi_stat_sum(bdi, BDI_RECLAIMABLE)), > K(bdi_thresh), K(dirty_thresh), > K(background_thresh), nr_wb, nr_dirty, nr_io, nr_more_io, > !list_empty(&bdi->bdi_list), bdi->state, bdi->wb_mask, > Is this really important? This patch is basically a local DoS for large machines. Imagine someone doing: while :; do cat /debug/bdi/*/stats; done on a 512 cpu box.