From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: what is the point of nr_pages information for the flusher thread? Date: Wed, 7 Jul 2010 19:16:11 -0400 Message-ID: <20100707231611.GA24281@infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org To: fengguang.wu@intel.com, mel@csn.ul.ie, akpm@linux-foundation.org, npiggin@suse.de Return-path: Received: from bombadil.infradead.org ([18.85.46.34]:33051 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757879Ab0GGXQh (ORCPT ); Wed, 7 Jul 2010 19:16:37 -0400 Content-Disposition: inline Sender: linux-fsdevel-owner@vger.kernel.org List-ID: Currently there's three possible values we pass into the flusher thread for the nr_pages arguments: - in sync_inodes_sb and bdi_start_background_writeback: LONG_MAX - in writeback_inodes_sb and wb_check_old_data_flush: global_page_state(NR_FILE_DIRTY) + global_page_state(NR_UNSTABLE_NFS) + (inodes_stat.nr_inodes - inodes_stat.nr_unused) - in wakeup_flusher_threads and laptop_mode_timer_fn: global_page_state(NR_FILE_DIRTY) + global_page_state(NR_UNSTABLE_NFS) The LONG_MAX cases are triviall explained, as we ignore the nr_to_write value for data integrity writepage in the lowlevel writeback code, and the for_background in bdi_start_background_writeback has it's own check for the background threshold. So far so good, and now it gets interesting. Why does writeback_inodes_sb add the number of used inodes into a value that is in units of pages? And why don't the other callers do this? But seriously, how is the _global_ number of dirty and unstable pages a good indicator for the amount of writeback per-bdi or superblock anyway? Somehow I'd feel much better about doing this calculation all the way down in wb_writeback instead of the callers so we'll at least have one documented place for these insanities.