That's what makes it so hard (at least for me) to reason about what workloads would get hurt, since there's not a simple, immediate relationship between "application dirtied a page" and "page got scheduled for writeback." You need both of those things to happen *and* the application must subsequently try to dirty the page further before you hit the page-block.
I guess you could get some negative interactions more immediately if a 'write' call scheduled a writeback for part of a page, and then the app immediately resumed filling the rest of the page. Still, I don't think a write() syscall triggers an immediate writeback on most calls. Take a look at 'queue_io' around line 277:
Only the oldest dirtied pages get flushed, as I read that.
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