From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from plane.gmane.org ([80.91.229.3]:56524 "EHLO plane.gmane.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751135AbaICFh7 (ORCPT ); Wed, 3 Sep 2014 01:37:59 -0400 Received: from list by plane.gmane.org with local (Exim 4.69) (envelope-from ) id 1XP3GV-00051D-2u for linux-btrfs@vger.kernel.org; Wed, 03 Sep 2014 07:37:55 +0200 Received: from ip68-231-22-224.ph.ph.cox.net ([68.231.22.224]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Wed, 03 Sep 2014 07:37:55 +0200 Received: from 1i5t5.duncan by ip68-231-22-224.ph.ph.cox.net with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Wed, 03 Sep 2014 07:37:55 +0200 To: linux-btrfs@vger.kernel.org From: Duncan <1i5t5.duncan@cox.net> Subject: Re: kernel 3.17-rc3: task rsync:2524 blocked for more than 120 seconds Date: Wed, 3 Sep 2014 05:37:43 +0000 (UTC) Message-ID: References: <540498AF.6030109@fb.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-btrfs-owner@vger.kernel.org List-ID: Chris Murphy posted on Tue, 02 Sep 2014 20:44:06 -0600 as excerpted: > On Sep 2, 2014, at 12:40 AM, Duncan <1i5t5.duncan@cox.net> wrote: >> >> Mkfs.btrfs used to default to 4 KiB node/leaf sizes; now days it >> defaults to 16 KiB as that's far better for most usage. I wonder if >> USB sticks are an exception… > > USB sticks > 1 GB get 16KB nodesize also. Seems you read into that a meaning I didn't even consider when I wrote it. =:^/ I /meant/ that AFAIK mkfs.btrfs did the usual 16K thing, but that perhaps (some, depending on erase-block size) USB sticks are an exception to 16K being better than 4K thing. > At <= 1 GB, mixed-bg is > default as is 4KB nodesize. Probably because queue/rotational is 1 for > USB sticks, they mount without ssd or ssd_spread which may be > unfortunate (I haven't benchmarked it but I suspect ssd_spread would > work well for USB sticks). I did mention ssd_spread somewhere in my replies, due to the same suspicion. Good to see you have the same suspicion I do. =:^) > It was suggested a while ago that maybe mixed-bg should apply to larger > volumes, maybe up to 8GB or 16GB? Indeed. Considering the default data chunk size is 1 GiB, that as the cutoff for default mixed-bg mode seems kinda low. If anything, I think 16 GiB is still a low cutoff value, at least as long as the only way to reclaim out-of-balance data/metadata assigned chunks is via a manual balance. I'd suggest a 32 GiB cutover by default. Tho if btrfs gets a good auto-balance-trigger mechanism that say triggers when allocated (fi show device figure) is within say 10% of total filesystem space (rounded up to the nearest GiB, minimum 2 GiB) AND data or metadata has more than say 10% spread between used and allocated (fi df, again rounded up, 2 GiB minimum), that can arguably come down a notch, to say 16 GiB. -- Duncan - List replies preferred. No HTML msgs. "Every nonfree program has a lord, a master -- and if you use the program, he is your master." Richard Stallman