linux-kernel - Re: [RFC 04/14] fork: Remove assumption that vm_area->nr_pages equals to THREAD

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Date: Sun, 17 Mar 2024 11:14:41 -0400
From: Pasha Tatashin <pasha.tatashin@...een.com>
To: Christophe JAILLET <christophe.jaillet@...adoo.fr>
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	tglx@...utronix.de, urezki@...il.com, vincent.guittot@...aro.org
Subject: Re: [RFC 04/14] fork: Remove assumption that vm_area->nr_pages equals
 to THREAD_SIZE

On Sun, Mar 17, 2024 at 10:45 AM Christophe JAILLET
<christophe.jaillet@...adoo.fr> wrote:
>
> Le 11/03/2024 à 17:46, Pasha Tatashin a écrit :
> > In many places number of pages in the stack is detremined via
> > (THREAD_SIZE / PAGE_SIZE). There is also a BUG_ON() that ensures that
> > (THREAD_SIZE / PAGE_SIZE) is indeed equals to vm_area->nr_pages.
> >
> > However, with dynamic stacks, the number of pages in vm_area will grow
> > with stack, therefore, use vm_area->nr_pages to determine the actual
> > number of pages allocated in stack.
> >
> > Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
> > ---
> >   kernel/fork.c | 18 +++++++++---------
> >   1 file changed, 9 insertions(+), 9 deletions(-)
> >
> > diff --git a/kernel/fork.c b/kernel/fork.c
> > index 60e812825a7a..a35f4008afa0 100644
> > --- a/kernel/fork.c
> > +++ b/kernel/fork.c
> > @@ -243,13 +243,11 @@ static int free_vm_stack_cache(unsigned int cpu)
> >
> >   static int memcg_charge_kernel_stack(struct vm_struct *vm)
>
> Maybe s/vm/vm_area/ as done in 03/14?

Yes, I will add it to 03/14.

Thank you,
Pasha

>
> CJ
>
> >   {
> > -     int i;
> > -     int ret;
> > +     int i, ret, nr_pages;
> >       int nr_charged = 0;
> >
> > -     BUG_ON(vm->nr_pages != THREAD_SIZE / PAGE_SIZE);
> > -
> > -     for (i = 0; i < THREAD_SIZE / PAGE_SIZE; i++) {
> > +     nr_pages = vm->nr_pages;
> > +     for (i = 0; i < nr_pages; i++) {
> >               ret = memcg_kmem_charge_page(vm->pages[i], GFP_KERNEL, 0);
> >               if (ret)
> >                       goto err;
> > @@ -531,9 +529,10 @@ static void account_kernel_stack(struct task_struct *tsk, int account)
> >   {
> >       if (IS_ENABLED(CONFIG_VMAP_STACK)) {
> >               struct vm_struct *vm = task_stack_vm_area(tsk);
> > -             int i;
> > +             int i, nr_pages;
> >
> > -             for (i = 0; i < THREAD_SIZE / PAGE_SIZE; i++)
> > +             nr_pages = vm->nr_pages;
> > +             for (i = 0; i < nr_pages; i++)
> >                       mod_lruvec_page_state(vm->pages[i], NR_KERNEL_STACK_KB,
> >                                             account * (PAGE_SIZE / 1024));
> >       } else {
> > @@ -551,10 +550,11 @@ void exit_task_stack_account(struct task_struct *tsk)
> >
> >       if (IS_ENABLED(CONFIG_VMAP_STACK)) {
> >               struct vm_struct *vm;
> > -             int i;
> > +             int i, nr_pages;
> >
> >               vm = task_stack_vm_area(tsk);
> > -             for (i = 0; i < THREAD_SIZE / PAGE_SIZE; i++)
> > +             nr_pages = vm->nr_pages;
> > +             for (i = 0; i < nr_pages; i++)
> >                       memcg_kmem_uncharge_page(vm->pages[i], 0);
> >       }
> >   }
>