Re: missing madvise functionality

[Eric Dumazet]

Ulrich Drepper a Ãcrit :
> Eric Dumazet wrote:
> > Database workload, where the user multi threaded app is constantly
> > accessing GBytes of data, so L2 cache hit is very small. If you want to
> > oprofile it, with say a CPU_CLK_UNHALTED:5000 event, then find_vma() is
> > in the top 5.
>
> We did have a workload with lots of Java and databases at some point
> when many VMAs were the issue.  I brought this up here one, maybe two
> years ago and I think Blaisorblade went on and looked into avoiding VMA
> splits by having mprotect() not split VMAs and instead store the flags
> in the page table somewhere.  I don't remember the details.
>
> Nothing came out of this but if this is possible it would be yet another
> way to avoid mmap_sem locking, right?

I was speaking about oprofile needs, that may interfere with target process 
needs, since oprofile calls find_vma() on the target process mm and thus zap 
its mmap_cache.

oprofile is yet another mmap_sem user, but also a mmap_cache destroyer.

We could at least have a separate cache, only for oprofile.

If done correctly we might avoid taking mmap_sem when the same vm_area_struct 
contains EIP/RIP snapshots.


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/