using writepage to start io
Quoted 7 lines · On Monday, August 06, 2001 11:18:26 PM +0200 Daniel Phillips…
Quoted 4 lines
Grin, we're talking in circles. My point is that by having two threads, bdflush is allowed to skip over older buffers in favor of younger ones because somebody else is responsible for writing the older ones out.
Yes, and you can't imagine an algorithm that could do that with *one* thread?
Imagine one? Yes. We're mixing a bunch of issues, so I'll list the 3 different cases again. memory pressure, write throttling, age limiting. Pretending that a single thread could get enough context information about which of the 3 (perhaps more than one) it is currently facing, it can make the right decisions.
The problem with that right now is that a single thread can't keep up (with one case, let alone all 3) as the number of devices increases. We can more or less just replay the entire l-k discussion(s) on threading models here.
In my mind, in order for a single thread to get the job done, it can't end up waiting on a device while there are still buffers ready for writeout to idle devices.
As for a generic mechanism to schedule all FS writeback, I've been trying to use writepage ;-) The bad part here it makes the async issues even bigger, since the flushing thread ends up calling into the FS (who knows what that might lead to).
-chris
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