slub: consider pfmemalloc_match() in get_partial_node()

slub: consider pfmemalloc_match() in get_partial_node()

get_partial() is currently not checking pfmemalloc_match() meaning that it
is possible for pfmemalloc pages to leak to non-pfmemalloc users.  This is
a problem in the following situation.  Assume that there is a request from
normal allocation and there are no objects in the per-cpu cache and no
node-partial slab.

In this case, slab_alloc enters the slow path and new_slab_objects() is
called which may return a PFMEMALLOC page.  As the current user is not
allowed to access PFMEMALLOC page, deactivate_slab() is called ([5091b74a:
mm: slub: optimise the SLUB fast path to avoid pfmemalloc checks]) and
returns an object from PFMEMALLOC page.

Next time, when we get another request from normal allocation,
slab_alloc() enters the slow-path and calls new_slab_objects().  In
new_slab_objects(), we call get_partial() and get a partial slab which was
just deactivated but is a pfmemalloc page.  We extract one object from it
and re-deactivate.

"deactivate -> re-get in get_partial -> re-deactivate" occures repeatedly.

As a result, access to PFMEMALLOC page is not properly restricted and it
can cause a performance degradation due to frequent deactivation.
deactivation frequently.

This patch changes get_partial_node() to take pfmemalloc_match() into
account and prevents the "deactivate -> re-get in get_partial() scenario.
Instead, new_slab() is called.

Signed-off-by: Joonsoo Kim <js1304@gmail.com>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Mel Gorman <mgorman@suse.de>
Cc: David Miller <davem@davemloft.net>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>