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    SubjectRe: controlling mmap()'d vs read/write() pages
    Eric W. Biederman wrote:
    > Nick Piggin <nickpiggin@yahoo.com.au> writes:
    >
    >
    >>Eric W. Biederman wrote:
    >>
    >>>Dave Hansen <hansendc@us.ibm.com> writes:
    >>>
    >>>
    >>>
    >>>>So, I think we have a difference of opinion. I think it's _all_ about
    >>>>memory pressure, and you think it is _not_ about accounting for memory
    >>>>pressure. :) Perhaps we mean different things, but we appear to
    >>>>disagree greatly on the surface.
    >>>
    >>>
    >>>I think it is about preventing a badly behaved container from having a
    >>>significant effect on the rest of the system, and in particular other
    >>>containers on the system.
    >>
    >>That's Dave's point, I believe. Limiting mapped memory may be
    >>mostly OK for well behaved applications, but it doesn't do anything
    >>to stop bad ones from effectively DoSing the system or ruining any
    >>guarantees you might proclaim (not that hard guarantees are always
    >>possible without using virtualisation anyway).
    >>
    >>This is why I'm surprised at efforts that go to such great lengths
    >>to get accounting "just right" (but only for mmaped memory). You
    >>may as well not even bother, IMO.
    >>
    >>Give me an RSS limit big enough to run a couple of system calls and
    >>a loop...
    >
    >
    > Would any of them work on a system on which every filesystem was on
    > ramfs, and there was no swap? If not then they are not memory attacks
    > but I/O attacks.
    >
    > I completely concede that you can DOS the system with I/O if that is
    > not limited as well.
    >
    > My point is that is not a memory problem but a disk I/O problem which is
    > much easier to and cheaper to solve. Disk I/O is fundamentally a slow
    > path which makes it hard to modify it in a way that negatively affects
    > system performance.
    >
    > I don't think with a memory RSS limit you can DOS the system in a way
    > that is purely about memory. You have to pick a different kind of DOS
    > attack.

    It can be done trivially without performing any IO or swap, yes.

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