On Fri, Jul 22 2016, NeilBrown wrote:

>
> Looking at the current code, __GFP_DIRECT_RECLAIM is disabled the first
> time through, but if the pool is empty, direct-reclaim is allowed on the
> next attempt.  Presumably this is where the throttling comes in ??  I
> suspect that it really shouldn't do that. It should leave kswapd to do
> reclaim (so __GFP_KSWAPD_RECLAIM is appropriate) and only wait in
> mempool_alloc where pool->wait can wake it up.

Actually, thinking about the kswapd connection, it might make sense
for mempool_alloc() to wait in the relevant pgdata->pfmemalloc_wait as
well as waiting on pool->wait.  What way it should be able to proceed as
soon as any memory is available.  I don't know what the correct 'pgdata'
is though.

Just a thought,
NeilBrown