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    SubjectRe: [RFC][PATCH] VM: per-user overcommit policy
    On Mon, May 07, 2007 at 08:56:39PM +0200, Andrea Righi wrote:
    > Allow to define per-UID virtual memory overcommit handling. Configuration is
    > stored in a hash list in kernel space reachable through /proc/overcommit_uid
    > (surely there're better ways to do it, i.e. via configfs).
    > Hash elements are defined using a triple:
    > uid:overcommit_memory:overcommit_ratio
    > The overcommit_* values have the same semantic of their respective sysctl
    > variables.
    > If a user is not present in the hash, the default system policy will be used
    > (defined by /proc/sys/vm/overcommit_memory and /proc/sys/vm/overcommit_ratio).

    While I think it's a step in the right direction, I'm not convinced of
    the soundness of the approach. I expect one might be better served by
    per-user limits on committed memory, perhaps even proportional limits.

    The basic idea is that committed memory is a relatively global resource.
    You can apportion it and limit the global pool, but it's difficult to
    arrange for overall overcommitment policy on a per-anything basis
    without some sort of OOM-isolated domains for users and processes to run
    within. Those are particularly interesting as they relate to kernel
    memory allocations.

    The /proc/ interface is probably going to raise a few eyebrows. I'm
    unaware of what sorts of interfaces would be recommended for all this.

    The following stanza occurs often:
    + if (!vm_acct_get_config(&v, current->uid)) {
    + overcommit_memory = v.overcommit_memory;
    + overcommit_ratio = v.overcommit_ratio;
    + } else {
    + overcommit_memory = sysctl_overcommit_memory;
    + overcommit_ratio = sysctl_overcommit_ratio;
    + }

    suggesting that vm_acct_get_config() isn't the proper abstraction.

    Instead of
    int vm_acct_get_config(struct vm_acct_values *, uid_t);
    you could just have
    int vm_acct_get_config(struct vm_acct_values *);
    which conditionally uses current->uid, and then unconditionally use
    v.overcommit_memory and v.overcommit_ratio vs. sysctl_overcommit_memory
    and sysctl_overcommit_ratio in the sequel.


    -- wli
    -
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