Messages in this thread | | | Date | Wed, 27 Aug 2014 18:30:27 -0700 | From | Andy Lutomirski <> | Subject | Re: [PATCH v10 00/21] Support ext4 on NV-DIMMs |
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On 08/27/2014 02:46 PM, Andrew Morton wrote: > I assume (because I wasn't told!) that there are two objectives here: > > 1) reduce memory consumption by not maintaining pagecache and > 2) reduce CPU cost by avoiding the double-copies. > > These things are pretty easily quantified. And really they must be > quantified as part of the developer testing, because if you find > they've worsened then holy cow, what went wrong. >
There are two more huge ones:
3) Writes via mmap are immediately durable (or at least they're durable after a *very* lightweight flush).
4) No page faults ever once a page is writable (I hope -- I'm not sure whether this series actually achieves that goal).
A note on #3: there is ongoing work to enable write-through memory for things like this. Once that's done, then writes via mmap might actually be synchronously durable, depending on chipset details.
--Andy
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