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    SubjectRe: [RFC] Limit the size of the pagecache
    On Wed, 24 Jan 2007 14:15:10 +0900
    KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:

    > - One for stability
    > When a customer constructs their detabase(Oracle), the system often goes to oom.
    > This is because that the system cannot allocate DMA_ZOME memory for 32bit device.
    > (USB or e100)
    > Not allowing to use almost all pages as page cache (for temporal use) will be some help.
    > (Note: construction DB on ext3....so all writes are serialized and the system couldn't
    > free page cache.)

    I'm surprised that any reasonable driver has a dependency on ZONE_DMA. Are
    you sure? Send full oom-killer output, please.


    > - One for tuing.
    > Sometimes our cutomer requests us to limit size of page-cache.
    >
    > Many cutomers's memory usage reaches 99.x%. (this is very common situation.)
    > If almost all memories are used by page-cache, and we can think we can free it.
    > But the customer cannot estimate what amount of page-cache can be freed (without
    > perfromance regression).
    >
    > When a cutomer wants to add a new application, he tunes the system.
    > But memory usage is always 99%.
    > page-cache limitation is useful when the customer tunes his system and find
    > sets of data and page-cache.
    > (Of course, we can use some other complicated resource management system for this.)
    > This will allow the users to decide that they need extra memory or not.
    >
    > And...some customers want to keep memory Free as much as possible.
    > 99% memory usage makes insecure them ;)

    Tell them to do "echo 3 > /proc/sys/vm/drop_caches", then wait three minutes?
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