Messages in this thread | | | Date | Sun, 11 Nov 2007 21:39:26 +0200 | From | Heikki Orsila <> | Subject | Re: Strage buffer behaviour |
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On Sun, Nov 11, 2007 at 07:33:35PM +0100, Tino Keitel wrote: > I noticed that the kernel (2.6.23.1) seems to buffer only certain > partitions on my system: > > $ for i in 1 2 3 4 ; do for j in 1 2 ; do dd if=/dev/sda$i of=/dev/null > bs=1024k count=100 ; done ; done > 100+0 records in > 100+0 records out > 104857600 bytes (105 MB) copied, 3.01471 seconds, 34.8 MB/s > 100+0 records in > 100+0 records out > 104857600 bytes (105 MB) copied, 2.86945 seconds, 36.5 MB/s > 100+0 records in > 100+0 records out > 104857600 bytes (105 MB) copied, 2.92038 seconds, 35.9 MB/s > 100+0 records in > 100+0 records out > 104857600 bytes (105 MB) copied, 3.00272 seconds, 34.9 MB/s > 100+0 records in > 100+0 records out > 104857600 bytes (105 MB) copied, 4.07722 seconds, 25.7 MB/s > 100+0 records in > 100+0 records out > 104857600 bytes (105 MB) copied, 0.0944248 seconds, 1.1 GB/s > 100+0 records in > 100+0 records out > 104857600 bytes (105 MB) copied, 5.61527 seconds, 18.7 MB/s > 100+0 records in > 100+0 records out > 104857600 bytes (105 MB) copied, 0.331822 seconds, 316 MB/s > > The dd command reads 100 MB from each partition two times in a row. It > looks like sda1 and sda2 are not bufferd (the first 4 dd runs), but > sda3 and sda4 are (the last 4 dd runs).
Strange.. I'm running 2.6.24-rc1 here. Reading data from /dev/hda1 caches well, but not from /dev/sd[ab]1.
PS. you can flush caches with:
echo 1 > /proc/sys/vm/drop_caches
-- Heikki Orsila Barbie's law: heikki.orsila@iki.fi "Math is hard, let's go shopping!" http://www.iki.fi/shd - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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