fork: optimize memcg_charge_kernel_stack() a bit

Since commit f1c1a9ee00e4 ("fork: Move memcg_charge_kernel_stack()
into CONFIG_VMAP_STACK"), memcg_charge_kernel_stack() has been moved
into CONFIG_VMAP_STACK block, so the CONFIG_VMAP_STACK check can be
removed.

Furthermore, memcg_charge_kernel_stack() is only invoked by
alloc_thread_stack_node() instead of dup_task_struct(). If
memcg_kmem_charge_page() fails, the uncharge process is handled in
memcg_charge_kernel_stack() itself instead of free_thread_stack(),
so remove the incorrect comments.

If memcg_charge_kernel_stack() fails to charge pages used by kernel
stack, only charged pages need to be uncharged. It's unnecessary to
uncharge those pages which memory cgroup pointer is NULL.

[[email protected]: remove assertion that PAGE_SIZE is a multiple of 1k]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Haifeng Xu <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Daniel Bristot de Oliveira <[email protected]>
Cc: Sebastian Andrzej Siewior <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions