RE: [PATCH 2/2] thp: support split page table lock

["Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>]

Naoya Horiguchi wrote:
> Thp related code also uses per process mm->page_table_lock now.
> So making it fine-grained can provide better performance.
> 
> This patch makes thp support split page table lock by using page->ptl
> of the pages storing "pmd_trans_huge" pmds.
> 
> Some functions like pmd_trans_huge_lock() and page_check_address_pmd()
> are expected by their caller to pass back the pointer of ptl, so this
> patch adds to those functions new arguments for that. Rather than that,
> this patch gives only straightforward replacement.
> 
> ChangeLog v3:
>  - fixed argument of huge_pmd_lockptr() in copy_huge_pmd()
>  - added missing declaration of ptl in do_huge_pmd_anonymous_page()
> 
> Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>

Generally, looks good. Few notes:

I believe you need to convert __pte_alloc() to new locking. Not sure about
__pte_alloc_kernel().
Have you check all rest mm->page_table_lock, that they shouldn't be
converted to new locking?

You use uninitialized_var() a lot. It's ugly. I've check few places
(task_mmu.c, copy_huge_pmd) and have found a reason why we need it there.
Why?

You often do

+       ptl = huge_pmd_lockptr(mm, pmd);
+       spin_lock(ptl);

Should we have a helper to combine them? huge_pmd_lock()?

-- 
 Kirill A. Shutemov

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