[PATCH 1/2] mm,thp: refactor generic deposit/withdraw routines for wider usage

[Vineet Gupta]

On Thursday 11 February 2016 03:52 PM, Martin Schwidefsky wrote:
> On Thu, 11 Feb 2016 14:58:26 +0530
> Vineet Gupta <Vineet.Gupta1 at synopsys.com> wrote:
> 
>> Generic pgtable_trans_huge_deposit()/pgtable_trans_huge_withdraw()
>> assume pgtable_t to be struct page * which is not true for all arches.
>> Thus arc, s390, sparch end up with their own copies despite no special
>> hardware requirements (unlike powerpc).
> 
> s390 does have a special hardware requirement. pgtable_t is an address
> for a 2K block of memory. It is *not* equivalent to a struct page *
> which refers to a 4K block of memory. That has been the whole point
> to introduce pgtable_t.

Actually my reference to hardware requirement was more like powerpc style save a
hash value some where etc.

Now pgtable_t need not be struct page * even if the actual sizes are same - e.g.
in ARC port I kept pgtable_t as pte_t * simply to avoid a few page_address() calls
in mm code (you could argue that is was a micro-optimization, anyways..)

So given I know nothing about s390 MMU internals, I still think you can switch to
the update generic version despite 2K vs. 4K. Agree ?

>> It seems massaging the code a bit can make it reusbale.
> 
> Imho the new code for asm-generic looks fine, as long as the override
> with __HAVE_ARCH_PGTABLE_DEPOSIT/__HAVE_ARCH_PGTABLE_WITHDRAW continues
> to work I do not mind.