Extended attribute values can be larger than a reasonable maximum size
for our btree items so we store xattrs in many items. The first pass at
this code used vmalloc to make it relatively easy to work with a
contiguous buffer that was cut up into multiple items.
The problem, of course, is that vmalloc() is expensive. Well, the
problem is that I always forget just how expensive it can be and use it
when I shouldn't. We had loads on high cpu count machines that were
catastrophically cpu bound on all the contentious work that vmalloc does
to maintain a coherent global address space.
This removes the use of vmalloc and only allocates a small buffer for
the first compound item. The later items directly reference regions of
value buffer rather than copying it to and from the large intermediate
vmalloced buffer.
Signed-off-by: Zach Brown <zab@versity.com>
4e8a088cc5