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    SubjectRe: [PATCH 3/6] ksm: change the KSM_REMOVE_MEMORY_REGION ioctl.
    On Wed, 6 May 2009, Izik Eidus wrote:
    >
    > We can first start with this ioctl interface, later when we add swapping to
    > the pages, we can have madvice, and still (probably easily) support the ioctls
    > by just calling from inside ksm the madvice functions for that specific
    > address)
    >
    > I want to see ksm use madvice, but i believe it require some more changes to
    > mm/*.c, so it probably better to start with merging it when it doesnt touch
    > alot of stuff outisde ksm.c, and then to add swapping and after that add
    > madvice support (when the pages are swappable, everyone can use it)
    >
    > What you think about that?

    I think it's the wrong order to follow.

    The /dev/ksm interface is fine for your use while it's out of tree,
    but we want to get the user interface right when bringing it into
    mainline. I recall Chris being very clear on that too.

    Changing from /dev/ksm to madvise() is not a lot of work, it's mainly
    a matter of deleting code, and tidying up interfaces which would need
    more work anyway (I haven't commented on your curious -EPERMs yet!).

    It doesn't involve whether you've enabled swapping or not - let's
    forget the CAP_IPC_LOCK idea, and delegate that issue to limitation
    via sysfs, along with the ability to limit wild overuse of the feature
    - permissions on a sysfs node or something else?

    It does nudge towards making some decisions which need to be made
    anyway - that tends to be what a correct interface forces upon you.
    Like the issue of whether to go on covering unmapped areas or not -
    though possibly we could put off that decision, if it's doc'ed
    for now.

    And if it only covers mapped areas, then there will need to be a
    VM_flag for it, mainly so mm can call into ksm.c when it's unmapped;
    but I don't see it sinking hooks deeply into mm/*.c.

    Hugh


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