From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with SMTP id ED3BB6B01AF for ; Tue, 22 Jun 2010 00:07:33 -0400 (EDT) Date: Tue, 22 Jun 2010 12:07:27 +0800 From: Wu Fengguang Subject: Re: [PATCH RFC] mm: Implement balance_dirty_pages() through waiting for flusher thread Message-ID: <20100622040727.GA14340@localhost> References: <1276797878-28893-1-git-send-email-jack@suse.cz> <1276856497.27822.1699.camel@twins> <20100621134238.GE3828@quack.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100621134238.GE3828@quack.suse.cz> Sender: owner-linux-mm@kvack.org To: Jan Kara Cc: Peter Zijlstra , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, hch@infradead.org, akpm@linux-foundation.org List-ID: On Mon, Jun 21, 2010 at 03:42:39PM +0200, Jan Kara wrote: > On Fri 18-06-10 12:21:37, Peter Zijlstra wrote: > > On Thu, 2010-06-17 at 20:04 +0200, Jan Kara wrote: > > > + if (bdi_stat(bdi, BDI_WRITTEN) >= bdi->wb_written_head) > > > + bdi_wakeup_writers(bdi); > > > > For the paranoid amongst us you could make wb_written_head s64 and write > > the above as: > > > > if (bdi_stat(bdi, BDI_WRITTEN) - bdi->wb_written_head > 0) > > > > Which, if you assume both are monotonic and wb_written_head is always > > within 2^63 of the actual bdi_stat() value, should give the same end > > result and deal with wrap-around. > > > > For when we manage to create a device that can write 2^64 pages in our > > uptime :-) > OK, the fix is simple enough so I've changed it, although I'm not > paranoic enough ;) (I actually did the math before writing that test). a bit more change :) type: - u64 wb_written_head + s64 wb_written_head resetting: - bdi->wb_written_head = ~(u64)0; + bdi->wb_written_head = 0; setting: bdi->wb_written_head = bdi_stat(bdi, BDI_WRITTEN) + wc->written; + bdi->wb_written_head |= 1; testing: if (bdi->wb_written_head && bdi_stat(bdi, BDI_WRITTEN) - bdi->wb_written_head > 0) This avoids calling into bdi_wakeup_writers() pointlessly when no one is being throttled (which is the normal case). Thanks, Fengguang -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org