Re: [RFT][PATCH 2/2] pagefault scalability alternative

[Nick Piggin <nickpiggin@yahoo.com.au>]

Hugh Dickins wrote:
> On Tue, 23 Aug 2005, Nick Piggin wrote:

>>I had preempt_disable() in tlb_gather_mmu which I thought was nice,
>>but maybe you don't?
> 
> 
> I most definitely agree.  tlb_gather_mmu uses smp_processor_id when it
> should be using get_cpu, we don't usually open code the preempt_disable.
> 

Yep.

> But there's a number of things peculiar about tlb_gather_mmu and friends
> (e.g. the rss but not anon_rss asymmetry; and what have those got to do
> with "tlb" anyway?), spread over several arches, I decided to stay away
> for now, go into all that at a later date.  What it should be doing
> about rss depends rather on what Christoph ends up with there.
> 

I agree. I think moving rss accounting out of the tlb operations
and into mm/memory.c is a good idea too. I don't think there are
any problems doing so, either.

But we won't get bogged down on that right now.

> 
>>>+#ifdef CONFIG_SPLIT_PTLOCK
>>>+#define __pte_lockptr(page)	((spinlock_t *)&((page)->private))
>>>+#define pte_lock_init(page)	spin_lock_init(__pte_lockptr(page))
>>>+#define pte_lock_deinit(page)	((page)->mapping = NULL)
>>
>>Do you mean page->private?
> 
> 
> No, it does mean page->mapping: depending on DEBUG options and whatnot,
> the spinlock_t might (currently, I think) be as many as 5 unsigned longs,
> hich happily just happen to fit into the unmodified 32-bit struct page,
> and the only "corruption" which actually matters is that freeing a page
> protests if page->mapping is found set.
> 

OK no worries. Just so long as you don't overwrite ->_count,
the lockless pagecache is happy ;)

Which brings up another issue - this surely conflicts rather
badly with PageReserved removal :( Not that there is anything
wrong with that, but I don't like to create these kinds of
problems for people...

Do we still want to remove PageReserved sooner rather than
later?

-- 
SUSE Labs, Novell Inc.

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