+ fork-optimize-memcg_charge_kernel_stack-a-bit.patch added to mm-nonmm-unstable branch

+ fork-optimize-memcg_charge_kernel_stack-a-bit.patch added to mm-nonmm-unstable branch

[Andrew Morton]

The patch titled
     Subject: fork: optimize memcg_charge_kernel_stack() a bit
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     fork-optimize-memcg_charge_kernel_stack-a-bit.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/fork-optimize-memcg_charge_kernel_stack-a-bit.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Haifeng Xu <haifeng.xu@shopee.com>
Subject: fork: optimize memcg_charge_kernel_stack() a bit
Date: Mon, 8 May 2023 06:44:58 +0000

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.

Link: https://lkml.kernel.org/r/20230508064458.32855-1-haifeng.xu@shopee.com
Signed-off-by: Haifeng 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: Andrew Morton <akpm@linux-foundation.org>
---

 kernel/fork.c |   11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

--- a/kernel/fork.c~fork-optimize-memcg_charge_kernel_stack-a-bit
+++ a/kernel/fork.c
@@ -252,23 +252,20 @@ static int memcg_charge_kernel_stack(str
 {
 	int i;
 	int ret;
+	int nr_charged = 0;
 
-	BUILD_BUG_ON(IS_ENABLED(CONFIG_VMAP_STACK) && PAGE_SIZE % 1024 != 0);
+	BUILD_BUG_ON(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;
 }
_

Patches currently in -mm which might be from haifeng.xu@shopee.com are

memcg-oom-remove-unnecessary-check-in-mem_cgroup_oom_synchronize.patch
memcg-oom-remove-explicit-wakeup-in-mem_cgroup_oom_synchronize.patch
mm-oom-do-not-check-0-mask-in-out_of_memory.patch
fork-optimize-memcg_charge_kernel_stack-a-bit.patch