Re: [PATCHv4 09/10] mm: implement split page table lock for PMDlevel

[Andrew Morton]

On Fri, 27 Sep 2013 16:16:26 +0300 "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> wrote:

> The basic idea is the same as with PTE level: the lock is embedded into
> struct page of table's page.
> 
> We can't use mm->pmd_huge_pte to store pgtables for THP, since we don't
> take mm->page_table_lock anymore. Let's reuse page->lru of table's page
> for that.
> 
> pgtable_pmd_page_ctor() returns true, if initialization is successful
> and false otherwise. Current implementation never fails, but assumption
> that constructor can fail will help to port it to -rt where spinlock_t
> is rather huge and cannot be embedded into struct page -- dynamic
> allocation is required.

spinlock_t is rather large when lockdep is enabled.  What happens?
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