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Date: Tue, 14 Aug 2012 12:59:48 +0200 From: Daniel Noack <fsf.deathman@...il.com> To: linux-kernel@...r.kernel.org Subject: Mmap on SSD (directly mapping the device vs. mapping a file) Hi, folks! First of all I have to say sorry that I'm not a subscriber of the list now, but I will subscribe in the near future (need an extra email account for it ;) ). It would be nice if you could put me on CC for an answer to my question. Like you can see on the subject I experimented a little bit with mmap in the last time. I've written a little B+tree library which uses mmap to store the tree to a file or the whole device (means it is also possible to map the hwole device (i.e. /dev/sdb)). I used msync after every successfull change on the tree. Next thing I did was to use this for a little benchmark on performance of different storage devices (ramdisk, HDD, and a very fast flashcard directly atteched to the PCIe bus). I recognized that in allmost all cases when directly mapping teh device without a filesystem the file-mapped version was a little bit slower. But when I tried it on an SSD device the file-mapped version was an order of magnitude faster. I also tried secure erase and did the benchmarks many times and in many configurations, but I came to the same results. Can anyone explain me what's happening here or have I something missed. Is this behavior correct? Thanks, Daniel -- 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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