On Mon, Jul 11, 2011 at 07:20:50PM +0200, Johannes Weiner wrote:

quoted

Yet the file pages on the active list are unlikely to be dirty -
overwrite-in-place cache hot workloads are pretty scarce in my
experience. hence writeback of dirty pages from the active LRU is
unlikely to be a problem.

Just to clarify, I looked at this too much from the reclaim POV, where
use-once applies to full pages, not bytes.

Even if you do not overwrite the same bytes over and over again,
issuing two subsequent write()s that end up against the same page will
have it activated.

Are your workloads writing in perfectly page-aligned chunks?

Many workloads do, given that we already tell them our preferred
I/O size through struct stat, which alway is the page size or larger.

That won't help with workloads having to write in small chunksizes.
The performance critical ones using small chunksizes usually use
O_(D)SYNC, so pages will be clean after the write returned to userspace.

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