s390/mm: implement software referenced bits

The last remaining use for the storage key of the s390 architecture is reference counting. The alternative is to make page table entries invalid while they are old. On access the fault handler marks the pte/pmd as young which makes the pte/pmd valid if the access rights allow read access. The pte/pmd invalidations required for software managed reference bits cost a bit of performance, on the other hand the RRBE/RRBM instructions to read and reset the referenced bits are quite expensive as well. Reviewed-by: Gerald Schaefer <[email protected]> Signed-off-by: Martin Schwidefsky <[email protected]>
kyagi · Aug 29, 2013 · 0944fe3 · 0944fe3
1 parent fbd7003
commit 0944fe3
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Showing 7 changed files with 244 additions and 194 deletions.
diff --git a/arch/s390/include/asm/page.h b/arch/s390/include/asm/page.h
@@ -140,15 +140,6 @@ static inline int page_reset_referenced(unsigned long addr)
 #define _PAGE_FP_BIT		0x08	/* HW fetch protection bit	*/
 #define _PAGE_ACC_BITS		0xf0	/* HW access control bits	*/
 
-/*
- * Test and clear referenced bit in storage key.
- */
-#define __HAVE_ARCH_PAGE_TEST_AND_CLEAR_YOUNG
-static inline int page_test_and_clear_young(unsigned long pfn)
-{
-	return page_reset_referenced(pfn << PAGE_SHIFT);
-}
-
 struct page;
 void arch_free_page(struct page *page, int order);
 void arch_alloc_page(struct page *page, int order);