Commit 4e2f6342 authored by Haifeng Xu's avatar Haifeng Xu Committed by Andrew Morton
Browse files

fork: optimize memcg_charge_kernel_stack() a bit 

Since commit f1c1a9ee ("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.

[akpm@linux-foundation.org: remove assertion that PAGE_SIZE is a multiple of 1k]
Link: https://lkml.kernel.org/r/20230508064458.32855-1-haifeng.xu@shopee.com


Signed-off-by: default avatarHaifeng Xu <haifeng.xu@shopee.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Daniel Bristot de Oliveira <bristot@kernel.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 3db55767

kernel/fork.c

+3 −7
Original line number Diff line number Diff line
@@ -252,23 +252,19 @@ static int memcg_charge_kernel_stack(struct vm_struct *vm) 
{

	int i;

	int ret;

	int nr_charged = 0;



	BUILD_BUG_ON(IS_ENABLED(CONFIG_VMAP_STACK) && PAGE_SIZE % 1024 != 0);

	BUG_ON(vm->nr_pages != THREAD_SIZE / PAGE_SIZE);



	for (i = 0; i < THREAD_SIZE / PAGE_SIZE; i++) {

		ret = memcg_kmem_charge_page(vm->pages[i], GFP_KERNEL, 0);

		if (ret)

			goto err;

		nr_charged++;

	}

	return 0;

err:

	/*

	 * If memcg_kmem_charge_page() fails, page's memory cgroup pointer is

	 * NULL, and memcg_kmem_uncharge_page() in free_thread_stack() will

	 * ignore this page.

	 */

	for (i = 0; i < THREAD_SIZE / PAGE_SIZE; i++)

	for (i = 0; i < nr_charged; i++)

		memcg_kmem_uncharge_page(vm->pages[i], 0);

	return ret;

}