mm: debugfs: move rounddown_pow_of_two() out from do_fault path (b4903d6e) · Commits · 戴 / test

do_fault_around() expects fault_around_bytes rounded down to nearest page order. Instead of calling rounddown_pow_of_two every time in fault_around_pages()/fault_around_mask() we could do round down when user changes fault_around_bytes via debugfs interface. This also fixes bug when user set fault_around_bytes to 0. Result of rounddown_pow_of_two(0) is not defined, therefore fault_around_bytes == 0 doesn't work without this patch. Let's set fault_around_bytes to PAGE_SIZE if user sets to something less than PAGE_SIZE [akpm@linux-foundation.org: tweak code layout] Fixes: ("mm: nominate faultaround area in bytes rather than page order") Signed-off-by:

Andrey Ryabinin <a.ryabinin@samsung.com> Reported-by:

Sasha Levin <sasha.levin@oracle.com> Acked-by:

Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: <stable@vger.kernel.org> [3.15.x] Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

mm/memory.c

+12 −9

Original line number	Diff line number	Diff line
		@@ -2758,23 +2758,18 @@ void do_set_pte(struct vm_area_struct *vma, unsigned long address,
		update_mmu_cache(vma, address, pte);
		}

		static unsigned long fault_around_bytes = 65536;
		static unsigned long fault_around_bytes = rounddown_pow_of_two(65536);

		/*
		* fault_around_pages() and fault_around_mask() round down fault_around_bytes
		* to nearest page order. It's what do_fault_around() expects to see.
		*/
		static inline unsigned long fault_around_pages(void)
		{
		return rounddown_pow_of_two(fault_around_bytes) / PAGE_SIZE;
		return fault_around_bytes >> PAGE_SHIFT;
		}

		static inline unsigned long fault_around_mask(void)
		{
		return ~(rounddown_pow_of_two(fault_around_bytes) - 1) & PAGE_MASK;
		return ~(fault_around_bytes - 1) & PAGE_MASK;
		}


		#ifdef CONFIG_DEBUG_FS
		static int fault_around_bytes_get(void data, u64 val)
		{
		@@ -2782,11 +2777,19 @@ static int fault_around_bytes_get(void data, u64 val)
		return 0;
		}

		/*
		* fault_around_pages() and fault_around_mask() expects fault_around_bytes
		* rounded down to nearest page order. It's what do_fault_around() expects to
		* see.
		*/
		static int fault_around_bytes_set(void *data, u64 val)
		{
		if (val / PAGE_SIZE > PTRS_PER_PTE)
		return -EINVAL;
		fault_around_bytes = val;
		if (val > PAGE_SIZE)
		fault_around_bytes = rounddown_pow_of_two(val);
		else
		fault_around_bytes = PAGE_SIZE; /* rounddown_pow_of_two(0) is undefined */
		return 0;
		}
		DEFINE_SIMPLE_ATTRIBUTE(fault_around_bytes_fops,

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