Re: [PATCH] mm: add sys_madvise2 and MADV_NAME to name vmas

[Oleg Nesterov <oleg@redhat.com>]

On 07/03, Colin Cross wrote:
>
> On Wed, Jul 3, 2013 at 9:54 PM, Eric W. Biederman <ebiederm@xmission.com> wrote:
> > Colin Cross <ccross@android.com> writes:
> >
> > What is the advantage of this?  It looks like it is going to add cache
> > line contention (atomic_inc/atomic_dec) to every vma operation
> > especially in the envision use case of heavy vma_name sharing.
> >
> > I would expect this will result in a bloated vm_area_struct and a slower
> > mm subsystem.
>
> The advantage is better tracking of the impact of various userspace
> allocations on the overall system.  Userspace could track allocations
> on its own, but it cannot track things like physical memory usage or
> Kernel SamePage Merging per allocation.

What I can't understand completely is why do you need the string to
mark the vma's.

Just make it "unsigned long vm_id" and avoid all these complications
with get/put and "struct vma_name". And afaics you can avoid other
complications too, the new argumnent for vma_merge() is not really
needed. This patch would be trivial.

> I expect "hand break" is overstating the impact.

The code complexity (and even size) does matter too ;) It is not clear
if this new feature worth the trouble.

Oleg.

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