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Linux Kernel Power Management Targeting Memory

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  • phoronix
    started a topic Linux Kernel Power Management Targeting Memory

    Linux Kernel Power Management Targeting Memory

    Phoronix: Linux Kernel Power Management Targeting Memory

    One of the areas of hardware power management that can yield a surprising amount of power-savings but is often overlooked comes down to the system memory. Fortunately, new Linux kernel patches continue to be written for improving the Linux kernel RAM power management...

    http://www.phoronix.com/vr.php?view=MTM0NzU

  • Ibidem
    replied
    Originally posted by schmidtbag View Post
    I'm not sure about that.... you can mount a tmpfs to any location you want and of any size you want. It is a RAM filesystem, it just doesn't dynamically expand like ramfs. I'm not sure of any simple way to directly access disk cache - it sounds like a severe security flaw to me.
    1: Sorry for the unclear wording: it is not the cache of another filesystem, but a "filesystem" backed only by RAM used by the disk caching code, as if you had a cache for another filesystem, but no file or device to back that:
    Originally posted by Documentation/fs/tmpfs.txt
    tmpfs puts everything into the kernel internal caches and grows and
    shrinks to accommodate the files it contains and is able to swap
    unneeded pages out to swap space. It has maximum size limits which can
    be adjusted on the fly via 'mount -o remount ...'
    2: It does dynamically expand, as written above. But it has limits. And that and whether it can swap are the main difference from ramfs. (ramfs does not swap.)

    (If you want a _good_ explanation, refer to the document within the kernel source tree having the name mentioned...)
    Last edited by Ibidem; 04-13-2013, 10:23 PM.

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  • schmidtbag
    replied
    Originally posted by Ibidem View Post
    The explanation I've heard is that tmpfs is just the disk cache, presented as a filesystem.
    Of course, caching in swap is rather pointless, though perhaps not entirely.
    I'm not sure about that.... you can mount a tmpfs to any location you want and of any size you want. It is a RAM filesystem, it just doesn't dynamically expand like ramfs. I'm not sure of any simple way to directly access disk cache - it sounds like a severe security flaw to me.

    Leave a comment:


  • Ibidem
    replied
    Originally posted by schmidtbag View Post
    That depends on your purpose, but generally speaking tmpfs is safer to use and makes more sense as a RAM drive. It'd be nice if there was a way to prevent tmpfs from accessing swap, but I personally never use swap so I guess I don't have much to worry about.
    The explanation I've heard is that tmpfs is just the disk cache, presented as a filesystem.
    Of course, caching in swap is rather pointless, though perhaps not entirely.

    Leave a comment:


  • schmidtbag
    replied
    Originally posted by Thaodan View Post
    Tmpfs is better than ramfs
    That depends on your purpose, but generally speaking tmpfs is safer to use and makes more sense as a RAM drive. It'd be nice if there was a way to prevent tmpfs from accessing swap, but I personally never use swap so I guess I don't have much to worry about.

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  • Thaodan
    replied
    Originally posted by Luke_Wolf View Post
    But.... RAMDrive....
    Tmpfs is better than ramfs

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  • curaga
    replied
    http://en.wikipedia.org/wiki/List_of_device_bit_rates

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  • schmidtbag
    replied
    Originally posted by curaga View Post
    There are pci-e ramdrives, and there's no need for RAID - even a single stick of DDR3 is faster than SATA-3.
    Have a link? And if you want a ram drive that isn't going to lose its data as soon as you power off then it doesn't matter how fast it is. What I'm thinking of is using a computer as a dedicated RAM drive, so if you could create a SATA connection then you can boot from it. Sure it won't be as fast as being directly on the board or on a PCIe bus but it'd be very "portable" and still faster than any other SSD.

    Leave a comment:


  • curaga
    replied
    There are pci-e ramdrives, and there's no need for RAID - even a single stick of DDR3 is faster than SATA-3.

    Leave a comment:


  • schmidtbag
    replied
    Originally posted by Luke_Wolf View Post
    But.... RAMDrive....
    RAM drives are nice, I even created an automated script to generate them, but I have yet to find a real practical use for them aside from live CDs. If there was a way to attach the RAM drive to at least 1 SATA port (but preferably more so I can do RAID 0) then RAM drives would be fantastic because then I could store an OS on them and boot from another computer. Imagine that though - a 4x RAID 0 RAM drive on SATA 3 - that's going to offer some performance you just simply can't beat.

    I'm really surprised someone hasn't created a SATA "bridge" like this yet. Or, a RAM drive that works this way. I'm sure it'd be wildly popular. The only true RAM drives that were made were SATAII and limited to like... 8GB. Modern SSDs are better, and cheaper.

    Leave a comment:

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