Messages in this thread | | | Date | Sun, 23 Oct 2005 14:27:12 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH 7/9] mm: split page table lock |
| |
Hugh Dickins <hugh@veritas.com> wrote: > > In this implementation, the spinlock is tucked inside the struct page of > the page table page: with a BUILD_BUG_ON in case it overflows - which it > would in the case of 32-bit PA-RISC with spinlock debugging enabled.
eh? It's going to overflow an unsigned long on x86 too:
typedef struct { raw_spinlock_t raw_lock; #if defined(CONFIG_PREEMPT) && defined(CONFIG_SMP) unsigned int break_lock; #endif #ifdef CONFIG_DEBUG_SPINLOCK unsigned int magic, owner_cpu; void *owner; #endif } spinlock_t;
I think we need a union here.
> +#define __pte_lockptr(page) ((spinlock_t *)&((page)->private)) > +#define pte_lock_init(_page) do { \ > + BUILD_BUG_ON((size_t)(__pte_lockptr((struct page *)0) + 1) > \ > + sizeof(struct page)); \
The above assumes that page.private is the final field in struct page. That's fragile.
> Splitting the lock is not quite for free: another cacheline access. > Ideally, I suppose we would use split ptlock only for multi-threaded > processes on multi-cpu machines; but deciding that dynamically would > have its own costs. So for now enable it by config, at some number > of cpus - since the Kconfig language doesn't support inequalities, let > preprocessor compare that with NR_CPUS. But I don't think it's worth > being user-configurable: for good testing of both split and unsplit > configs, split now at 4 cpus, and perhaps change that to 8 later.
I'll make it >= 2 for -mm.
> +#define __pte_lockptr(page) ((spinlock_t *)&((page)->private)) > +#define pte_lock_init(_page) do { \ > + BUILD_BUG_ON((size_t)(__pte_lockptr((struct page *)0) + 1) > \ > + sizeof(struct page)); \ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |