On Sat, 2011-04-16 at 10:44 +0100, Matt Fleming wrote:
> > static inline void pgtable_page_dtor(struct mm_struct *mm, struct page *page)
> > {
> > pte_lock_deinit(page);
> > + dec_mm_counter(mm, MM_PTEPAGES);
> > dec_zone_page_state(page, NR_PAGETABLE);
> > }
>
> I'm probably missing something really obvious but...
>
> Is this safe in the non-USE_SPLIT_PTLOCKS case? If we're not using
> split-ptlocks then inc/dec_mm_counter() are only safe when done under
> mm->page_table_lock, right? But it looks to me like we can end up doing,
>
> __pte_alloc()
> pte_alloc_one()
> pgtable_page_ctor()
>
> before acquiring mm->page_table_lock in __pte_alloc().
No, it's probably not safe. We'll have to come up with something a bit
different in that case. Either that, or just kill the non-atomic case.
Surely there's some percpu magic counter somewhere in the kernel that is
optimized for fast (unlocked?) updates and rare, slow reads.
-- Dave
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