Benjamin LaHaise wrote:

On Wed, Jul 31, 2002 at 01:06:12PM -0700, William Lee Irwin III wrote:

quoted

I'm not a fan of this kind of global decision. For example, I/O devices
may be fast enough and memory small enough to dump all memory in < 1s,
in which case dirtying most or all of memory is okay from a latency
standpoint, or it may take hours to finish dumping out 40% of memory,
in which case it should be far more eager about writeback.

Why?  Filling the entire ram with dirty pages is okay, and in fact you
want to support that behaviour for apps that "just fit" (think big
scientific apps).  The only interesting point is that when you hit the
limit of available memory, the system needs to block on *any* io
completing and resulting in clean memory (which is reasonably low
latency), not a specific io which may have very high latency.

I hear what you say.  Sometimes we want to allow a lot of
writeback buffering.  But sometimes we don't.

But let's back off a bit.   The problem is that a process
doing a large write() can penalise innocent processes which
want to allocate memory.

How to fix that?
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