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    SubjectRe: %u-order allocation failed
    > > It is perfectly OK to have a bit slower access to task_struct with
    > > probability 1/1000000.
    >
    > Except that you added a bug where some old driver code would crash the
    > machine by doing so.

    ?

    > > Yes, but there are still other dangerous usages of kmalloc and
    > > __get_free_pages. (The most offending one is in select.c)
    >
    > Nothing dangeorus there. The -ac vm isnt triggering these cases.

    Sorry, but it can be triggered by _ANY_ VM since buddy allocator was
    introduced. You have no guarantee, that you find two or more consecutive
    free pages. And if you don't, poll() fails.

    > > not abort his operation when it happens. Instead - they are trying to make
    > > high-order allocations fail less often :-/ How should random
    > > Joe-driver-developer know, that kmalloc(4096) is safe and kmalloc(4097) is
    > > not?
    >
    > 4096 is not safe - there is no safe size for a kmalloc, you can always run
    > out of memory - deal with it.

    This is not about running out of memory. It is about free space
    fragmentation. Think this:

    You have no swap.
    Program allocates one file cache page, one anon page, one cache page, one
    anon page and so on. The memory will look like:

    cache page
    anon page
    cache page
    anon page
    cache page
    anon page
    etc.

    Now some driver wants to allocate 4097 and it CAN'T. Even when there's
    half memory free.

    Mikulas


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