On Tue, 9 Jan 2007, Neil Brown wrote:
> Imagine a machine with lots of memory - say 100Gig.
i've had these problems on machines as "small" as 8GiB. the real problem
is that the kernel will let millions of potential (write) IO ops stack up
for a device which can handle only mere 100s of IOs per second. (and i'm
not convinced it does the IOs in a sane order when it has millions to
choose from)
replacing the percentage based dirty_ratio / dirty_background_ratio with
sane kibibyte units is a good fix... but i'm not sure it's sufficient.
it seems like the "flow control" mechanism (i.e. dirty_ratio) should be on
a device basis...
try running doug ledford'd memtest.sh on an 8GiB box with a single disk,
let it go a few minutes then ^C and type "sync". i've had to wait 10
minutes (2.6.18 with default vm settings).
it makes it hard to guarantee a box can shutdown quickly -- nasty for
setting up UPS on-battery timeouts for example.
-dean
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