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    SubjectRe: [PATCH 1/2] gfp: add __GFP_NOACCOUNT
    On Wed, May 06, 2015 at 01:59:41PM +0200, Michal Hocko wrote:
    > On Tue 05-05-15 12:45:42, Vladimir Davydov wrote:
    > > Not all kmem allocations should be accounted to memcg. The following
    > > patch gives an example when accounting of a certain type of allocations
    > > to memcg can effectively result in a memory leak.
    >
    > > This patch adds the __GFP_NOACCOUNT flag which if passed to kmalloc
    > > and friends will force the allocation to go through the root
    > > cgroup. It will be used by the next patch.
    >
    > The name of the flag is way too generic. It is not clear that the
    > accounting is KMEMCG related. __GFP_NO_KMEMCG sounds better?
    >
    > I was going to suggest doing per-cache rather than gfp flag and that
    > would actually work just fine for the kmemleak as it uses its own cache
    > already. But the ida_simple_get would be trickier because it doesn't use
    > any special cache and more over only one user seem to have a problem so
    > this doesn't sound like a good fit.

    I don't think making this flag per-cache is an option either, but for
    another reason - it would not be possible to merge such a kmem cache
    with caches without this flag set. As a result, total memory pressure
    would increase, even for setups without kmem-active memory cgroups,
    which does not sound acceptable to me.

    >
    > So I do not object to opt-out for kmemcg accounting but I really think
    > the name should be changed.

    I named it __GFP_NOACCOUNT to match with __GFP_NOTRACK, which is a very
    specific flag too (kmemcheck), nevertheless it has a rather generic
    name.

    Anyways, what else apart from memcg can account kmem so that we have to
    mention KMEMCG in the flag name explicitly?

    Thanks,
    Vladimir


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