On Tue, 25 May 2021, Vlastimil Babka wrote:

Slub has a static spinlock protected bitmap for marking which objects are on
freelist when it wants to list them, for situations where dynamically
allocating such map can lead to recursion or locking issues, and on-stack
bitmap would be too large.

The handlers of sysfs files alloc_calls and free_calls also currently use this
shared bitmap, but their syscall context makes it straightforward to allocate a
private map before entering locked sections, so switch these processing paths
to use a private bitmap.

Right in that case a GFP_KERNEL allocation is fine and you can avoid the
static map.

Acked-by: Christoph Lameter <redacted>