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Commit 8892d854 authored by Anton Ivanov's avatar Anton Ivanov Committed by Richard Weinberger
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um: Avoid marking pages with "changed protection" 



Changing protection is a very high cost operation in UML
because in addition to an extra syscall it also interrupts
mmap merge sequences generated by the tlb.

While the condition is not particularly common it is worth
avoiding.

Signed-off-by: default avatarAnton Ivanov <anton.ivanov@cambridgegreys.com>
Signed-off-by: default avatarRichard Weinberger <richard@nod.at>
parent 38e3cbd9

arch/um/include/asm/pgtable.h

+8 −1
Original line number Diff line number Diff line
@@ -197,12 +197,17 @@ static inline pte_t pte_mkold(pte_t pte) 


static inline pte_t pte_wrprotect(pte_t pte)

{ 

	if (likely(pte_get_bits(pte, _PAGE_RW)))

		pte_clear_bits(pte, _PAGE_RW);

	else

		return pte;

	return(pte_mknewprot(pte)); 

}



static inline pte_t pte_mkread(pte_t pte)

{ 

	if (unlikely(pte_get_bits(pte, _PAGE_USER)))

		return pte;

	pte_set_bits(pte, _PAGE_USER);

	return(pte_mknewprot(pte)); 

}
@@ -221,6 +226,8 @@ static inline pte_t pte_mkyoung(pte_t pte) 


static inline pte_t pte_mkwrite(pte_t pte)	

{

	if (unlikely(pte_get_bits(pte,  _PAGE_RW)))

		return pte;

	pte_set_bits(pte, _PAGE_RW);

	return(pte_mknewprot(pte)); 

}