Em Fri, Nov 20, 2015 at 09:25:36PM +0800, Wangnan (F) escreveu:
> >+ case BPF_MAP_PRIV_KEY_INDICS:
> >+ for (i = 0; i < priv->key.indics.nr_indics; i++) {
> >+ u64 _idx = priv->key.indics.indics[i];
> >+ unsigned int idx = (unsigned int)(_idx);
> >+
> >+ err = (*func)(name, map_fd, &def,
> >+ priv, &idx, arg);
> >+ if (err) {
> >+ pr_debug("ERROR: failed to insert value
> >to %s[%u]\n",
> >+ name, idx);
> >+ return err;
> >+ }
> >+ }
>
> This for-loop has a potential problem that, if perf's user want to
> set a very big array using indices, for example:
>
> # perf record -e
> mybpf.c/maps:mymap:values[1,2,3,10-100000,200000-400000]=3/
> mybpf.c/maps:mymap:values[100000-200000]=3/ ...
>
> Perf would alloc nearly 300000 slots for indices array, consume too much
> memory.
>
> I will fix this problem by reinterprete indices array, makes negative
> value represent range start and use next slot to store range size. For
> example, the above perf cmdline can be converted to:
>
> {1,2,3,-10, 99991,-200000,200001} and {-100000,100001}.
Why is that changing the way you specify what entries should be set to
a value will make it not allocate too much memory?
I found the first form of representing ( start-end ) to be better than (
-start, size ), but I would use what the C language uses for expressing
ranges in switch case ranges, which is familiar and doesn't reuses the
minus arithmetic operator to express a range, i.e.:
# perf record -e \
mybpf.c/maps:mymap:values[1,2,3,10..100000,200000..400000]=3/
# perf record -e \
mybpf.c/maps:mymap:values[100000..200000]=3/ ...
- Arnaldo
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