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Date: Wed, 27 Aug 2014 18:30:27 -0700 From: Andy Lutomirski <luto@...capital.net> To: Andrew Morton <akpm@...ux-foundation.org>, Matthew Wilcox <willy@...ux.intel.com> CC: Matthew Wilcox <matthew.r.wilcox@...el.com>, linux-fsdevel@...r.kernel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH v10 00/21] Support ext4 on NV-DIMMs 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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