Comment 3 for bug 1589563

A possible problem is dm_crypt works all trying to allocate pages in bio_alloc_bioset. Based on comments around relevant code allocation is supposed to come from a memory pool. But stacktraces show that code end ups to page allocator. I'm not familiar with relevant code paths so I need to read the code more carefully to figure out what actually blocks dm_crypt works the way they are blocked in stacktraces.