From f7b0ff2bc91d8bb2ba9fdb182da39dd9733b1c50 Mon Sep 17 00:00:00 2001 From: Linus Walleij Date: Fri, 9 May 2025 09:25:09 +0200 Subject: [PATCH] fork: define a local GFP_VMAP_STACK The current allocation of VMAP stack memory is using (THREADINFO_GFP & ~__GFP_ACCOUNT) which is a complicated way of saying (GFP_KERNEL | __GFP_ZERO): : define THREADINFO_GFP (GFP_KERNEL_ACCOUNT | __GFP_ZERO) : define GFP_KERNEL_ACCOUNT (GFP_KERNEL | __GFP_ACCOUNT) This is an unfortunate side-effect of independent changes blurring the picture: commit 19809c2da28aee5860ad9a2eff760730a0710df0 changed (THREADINFO_GFP | __GFP_HIGHMEM) to just THREADINFO_GFP since highmem became implicit. commit 9b6f7e163cd0f468d1b9696b785659d3c27c8667 then added stack caching and rewrote the allocation to (THREADINFO_GFP & ~__GFP_ACCOUNT) as cached stacks need to be accounted separately. However that code, when it eventually accounts the memory does this: ret = memcg_kmem_charge(vm->pages[i], GFP_KERNEL, 0) so the memory is charged as a GFP_KERNEL allocation. Define a unique GFP_VMAP_STACK to use GFP_KERNEL | __GFP_ZERO and move the comment there. Link: https://lkml.kernel.org/r/20250509-gfp-stack-v1-1-82f6f7efc210@linaro.org Signed-off-by: Linus Walleij Reported-by: Mateusz Guzik Cc: Pasha Tatashin Cc: Mike Rapoport (Microsoft) Signed-off-by: Andrew Morton --- kernel/fork.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) diff --git a/kernel/fork.c b/kernel/fork.c index 5fd893c907a5e..6616d173307a9 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -201,6 +201,12 @@ static inline void free_task_struct(struct task_struct *tsk) */ #define NR_CACHED_STACKS 2 static DEFINE_PER_CPU(struct vm_struct *, cached_stacks[NR_CACHED_STACKS]); +/* + * Allocated stacks are cached and later reused by new threads, so memcg + * accounting is performed by the code assigning/releasing stacks to tasks. + * We need a zeroed memory without __GFP_ACCOUNT. + */ +#define GFP_VMAP_STACK (GFP_KERNEL | __GFP_ZERO) struct vm_stack { struct rcu_head rcu; @@ -307,13 +313,8 @@ static int alloc_thread_stack_node(struct task_struct *tsk, int node) return 0; } - /* - * Allocated stacks are cached and later reused by new threads, - * so memcg accounting is performed manually on assigning/releasing - * stacks to tasks. Drop __GFP_ACCOUNT. - */ stack = __vmalloc_node(THREAD_SIZE, THREAD_ALIGN, - THREADINFO_GFP & ~__GFP_ACCOUNT, + GFP_VMAP_STACK, node, __builtin_return_address(0)); if (!stack) return -ENOMEM; -- 2.47.2