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    SubjectRe: [PATCH v6 0/5] zram/zsmalloc promotion
    Hi,

    On Fri, Aug 16, 2013 at 10:02:08AM +0800, Wanpeng Li wrote:
    > Hi Minchan,
    > On Thu, Aug 15, 2013 at 01:17:53AM +0900, Minchan Kim wrote:
    > >Hi Luigi,
    > >
    > >On Wed, Aug 14, 2013 at 08:53:31AM -0700, Luigi Semenzato wrote:
    > >> During earlier discussions of zswap there was a plan to make it work
    > >> with zsmalloc as an option instead of zbud. Does zbud work for
    > >
    > >AFAIR, it was not an optoin but zsmalloc was must but there were
    > >several objections because zswap's notable feature is to dump
    > >compressed object to real swap storage. For that, zswap needs to
    > >store bounded objects in a zpage so that dumping could be bounded, too.
    > >Otherwise, it could encounter OOM easily.
    > >
    > >> compression factors better than 2:1? I have the impression (maybe
    > >> wrong) that it does not. In our use of zram (Chrome OS) typical
    > >
    > >Since zswap changed allocator from zsmalloc to zbud, I didn't follow
    > >because I had no interest of low compressoin ratio allocator so
    > >I have no idea of status of zswap at a moment but I guess it would be
    > >still 2:1.
    > >
    > >> overall compression ratios are between 2.5:1 and 3:1. We would hate
    > >> to waste that memory if we switch to zswap.
    > >
    > >If you have real swap storage, zswap might be better although I have
    > >no number but real swap is money for embedded system and it has sudden
    > >garbage collection on firmware side if we use eMMC or SSD so that it
    > >could affect system latency. Morever, if we start to use real swap,
    > >maybe we should encrypt the data and it would be severe overhead(CPU
    > >and Power).
    > >
    >
    > Why real swap for embedded system need encrypt the data? I think there
    > is no encrypt for data against server and desktop.

    I have used some portable device but suddenly, I lost it or was stolen.
    A hacker can pick it up and read my swap and found my precious information.
    I don't want it. I guess it's one of reason ChromeOS don't want to use real
    swap.

    https://groups.google.com/a/chromium.org/forum/#!msg/chromium-os-discuss/92Fvi4Ezego/ZvbrC3L2FG4J

    >
    > >And what I am considering after promoting for zram feature is
    > >asynchronous I/O and it's possible because zram is block device.
    > >
    > >Thanks!
    > >--
    > >Kind regards,
    > >Minchan Kim
    > >
    > >--
    > >To unsubscribe, send a message with 'unsubscribe linux-mm' in
    > >the body to majordomo@kvack.org. For more info on Linux MM,
    > >see: http://www.linux-mm.org/ .
    > >Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
    >

    --
    Kind regards,
    Minchan Kim


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