Re: Linux-2.2.0 bad VM behaviour "dd if=/dev/zero of=/dev/hdc bs=256k"

Petri Mattila (petri@prihateam.fi)
Thu, 28 Jan 1999 20:48:40 +0200

>With DMA enabled, it will be much more likely that you have other
>processes trying to get memory while the IO is active, and that
>concurrency means that the mm layer is probably much more likely to see
>pages in the "locked" phase - which in turn means that we're less likely
>to free them, which results in us being more eager to free something else
>(ie page out stuff).

This sounds reasonable...

>Yes, all conjecture, and it's probably not exactly right, but something
>along these lines is probably what is going on. Timing and concurrency
>differences changing the way the system behaves.

... but I have difficulties to understand why page out in order to free
memory
for IO buffers. IMHO, It is ok to use all FREE (=not used by any process)
memory for buffers, but freeing more memory by paging and then use
it as IO buffers sounds overkill.

And yes, I know nothing about VM internals, so please excuse me if this
is just plain bulshit :-)

-- Petri

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