Messages in this thread | | | Date | Thu, 25 Jul 2013 15:27:19 -0400 | From | Dhaval Giani <> | Subject | Re: [RFC/PATCH 0/2] ext4: Transparent Decompression Support |
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On 2013-07-25 1:53 PM, Jörn Engel wrote: > On Thu, 25 July 2013 09:42:18 -0700, Taras Glek wrote: >> Footprint wins are useful on android, but it's the >> increased IO throughput on crappy storage devices that makes this >> most attractive. > All the world used to be a PC. Seems to be Android these days. > > The biggest problem with compression support in the past was the > physical properties of hard drives (the spinning type, if you can > still remember those). A random seek is surprisingly expensive, of a > similar cost to 1MB or more of linear read. So anything that > introduces more random seeks will kill the preciously little > performance you had to begin with. > > As long as files are write-once and read-only from that point on, you > can just append a bunch of compressed chunks on the disk and nothing > bad happens. But if you have a read-write file with random overwrites > somewhere in the middle, those overwrites will change the size of the > compressed data. You have to free the old physical blocks on disk and > allocate new ones. In effect, you have auto-fragmentation. > > So if you want any kind of support for your approach, I suspect you > should either limit it to write-once files or prepare for a mob of > gray-haired oldtimers with rainbow suspenders complaining about > performance on their antiquated hardware. And the mob may be larger > than you think.
Yes, we plan to limit it to write-once. In order to write, you have to replace the file.
Dhaval -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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