Re: [PATCH v2 01/13] mm: support madvise(MADV_FREE)

Hi Sergey,

On Wed, Nov 04, 2015 at 11:16:24AM +0900, Sergey Senozhatsky wrote:

Hi Minchan,

On (11/04/15 10:25), Minchan Kim wrote:
[..]

quoted

+static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
+                               unsigned long end, struct mm_walk *walk)
+

...

quoted

+	if (pmd_trans_unstable(pmd))
+		return 0;

I think it makes sense to update pmd_trans_unstable() and
pmd_none_or_trans_huge_or_clear_bad() comments in asm-generic/pgtable.h
Because they explicitly mention MADV_DONTNEED only. Just a thought.

Hmm, When I read comments(but actually I don't understand it 100%), it
says pmd disappearing from MADV_DONTNEED with mmap_sem read-side
lock. But MADV_FREE doesn't remove the pmd. So, I don't understand
what I should add comment. Please suggest if I am missing something.

quoted

@@ -379,6 +502,14 @@ madvise_vma(struct vm_area_struct *vma, struct vm_area_struct **prev,
 		return madvise_remove(vma, prev, start, end);
 	case MADV_WILLNEED:
 		return madvise_willneed(vma, prev, start, end);
+	case MADV_FREE:
+		/*
+		 * XXX: In this implementation, MADV_FREE works like

		  ^^^^
		XXX

What does it mean?

quoted

+		 * MADV_DONTNEED on swapless system or full swap.
+		 */
+		if (get_nr_swap_pages() > 0)
+			return madvise_free(vma, prev, start, end);
+		/* passthrough */

	-ss