From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with SMTP id 340B86B01EF for ; Tue, 20 Apr 2010 03:56:20 -0400 (EDT) Message-ID: <4BCD5E47.4020507@gmx.at> Date: Tue, 20 Apr 2010 09:56:55 +0200 From: Walter Haidinger MIME-Version: 1.0 Subject: Re: [Bugme-new] [Bug 15783] New: slow dd and multiple "page allocation failure" messages References: <20100419140948.0b748c69.akpm@linux-foundation.org> In-Reply-To: <20100419140948.0b748c69.akpm@linux-foundation.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Andrew Morton Cc: linux-mm@kvack.org, bugzilla-daemon@bugzilla.kernel.org, bugme-daemon@bugzilla.kernel.org List-ID: Am 19.04.2010 23:09, schrieb Andrew Morton: > > (switched to email. Please respond via emailed reply-to-all, not > via the bugzilla web interface). ok. > Sigh. This shouldn't happen. > > I'm going to go ahead and assume that some earlier kernels didn't > do this :( No, I don't _think_ so. Problem is, I only noticed this when zeroing out the device. Haven't done this recently with earlier kernels. Besides, as reported, not all write operations are slow. > Is the writeout to /dev/sde1 slow right from the start, or does it > start out fast and later slow down? It seems to me that write speed does not change very much, but the actual speed varies. One time it's just 10 MiB/s, another time about 30. But for a couple of tests writes, speed is pretty stable. Also, only writing directly to the device seems to be slow. Perhaps that's why is hard to notice. e.g.: when /dev/sde1 is mounted as ext3 fs: Copying a 5 GiB file takes about 50s, mbuffer /mnt1/foo1 writes with >100 MiB/s, dd if=/dev/zero of=/mnt1/foo2 manages >75 MiB/s. After unmounting and writing directly from /dev/zero to /dev/sde1: mbuffer writes about 40 MiB/s and dd less than 30. But then badblocks -svw -t 0x00 /dev/sde1 writes about 120 MiB/s. Btw, dd if=/dev/zero of=/dev/null runs with >500 MiB/s. Needless to say, I'm confused by the numbers... > `dd' isn't very efficient without the `bs' option - it reads and > writes in 512-byte chunks. But that shouldn't be causing these > problems. Tried mbuffer instead. Shows similar results, only a bit faster. Still, even if dd is inefficient, it is way slower than expected. If you want me to test anything, please let me know. Walter PS: The short tests above triggered no "page allocation failures" (vm.vfs_cache_pressure = 1000). -- 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