Re: [PATCH] lazy freeing of memory through MADV_FREE 2/2

Rik van Riel
2007-04-19T21:15:28Z

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Restore MADV_DONTNEED to its original Linux behaviour. This is still
not the same behaviour as POSIX, but applications may be depending on
the Linux behaviour already. Besides, glibc catches POSIX_MADV_DONTNEED
and makes sure nothing is done...

Signed-off-by: Rik van Riel <riel@redhat.com>

---
This is to be applied over of the original MADV_FREE patch.
It turns out that the current glibc patch already falls back
to MADV_DONTNEED if it gets an -EINVAL.

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--- linux-2.6.20.x86_64/mm/madvise.c.madv_free 2007-04-19 16:46:22.000000000 -0400
+++ linux-2.6.20.x86_64/mm/madvise.c 2007-04-19 16:52:19.000000000 -0400
@@ -130,7 +130,8 @@ static long madvise_willneed(struct vm_a
*/
static long madvise_dontneed(struct vm_area_struct * vma,
struct vm_area_struct ** prev,
- unsigned long start, unsigned long end)
+ unsigned long start, unsigned long end,
+ int behavior)
{
*prev = vma;
if (vma->vm_flags & (VM_LOCKED|VM_HUGETLB|VM_PFNMAP))
@@ -142,12 +143,14 @@ static long madvise_dontneed(struct vm_a
.last_index = ULONG_MAX,
};
zap_page_range(vma, start, end - start, &details);
- } else {
+ } else if (behavior == MADV_FREE) {
struct zap_details details = {
.madv_free = 1,
};
zap_page_range(vma, start, end - start, &details);
- }
+ } else /* behavior == MADV_DONTNEED */
+ zap_page_range(vma, start, end - start, NULL);
+
return 0;
}

@@ -219,10 +222,9 @@ madvise_vma(struct vm_area_struct *vma,
error = madvise_willneed(vma, prev, start, end);
break;

- /* FIXME: POSIX says that MADV_DONTNEED cannot throw away data. */
case MADV_DONTNEED:
case MADV_FREE:
- error = madvise_dontneed(vma, prev, start, end);
+ error = madvise_dontneed(vma, prev, start, end, behavior);
break;