Re: I/O very slow under 2.4 (device reading)

From: Linus Torvalds (
Date: Wed Aug 08 2001 - 13:12:40 EST

In article <20010808193158.A4055@cerebro.laendle>,
 < ( Marc) (A.) (Lehmann )> wrote:
>It might be vm related, it might be not, but I get very funny effects when
> buffer -S1m -s128k -m32m </dev/hde >/dev/null
>(buffer is just a fast read/write buffer reading stdin to stdout, i use it
>to check wether all sectors of a disk are readable, it's similar to dd,
>which creates the same effects).

I bet it's the same thing that made writes slow - the buffer allocator
and the VM disagree about how/when to allocate memory. It's fixed by the patch
that's floating around in the "VM suckage" thread along with the tweak
to fix "zone_free_plenty()".

I'll make a real pre-patch (2.4.8-pre7) with the full changeset, can you
test that out? I did an equivalent "dd" that you see problems with, and
on my current kernel as long as there isn't other IO activity it stays
at a nice stable 21MB/s which is all my disk can deliver.

[ Damn, maybe I should get one of those nice big 7200 rpm IBM drives ]

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This archive was generated by hypermail 2b29 : Wed Aug 15 2001 - 21:00:19 EST