From: Hugh Dickins <hugh@veritas.com>
Traditionally we've not flushed TLB after clearing the young/referenced bit,
it has seemed just a waste of time. Russell King points out that on some
architectures, with the move from 2.4 mm sweeping to 2.6 rmap, this may be a
serious omission: very frequently referenced pages never re-marked young, and
the worst choices made for unmapping.
So, replace ptep_test_and_clear_young by ptep_clear_flush_young throughout
rmap.c. Originally I'd imagined making some kind of TLB gather optimization,
but don't see what now: whether worth it rather depends on how common
cross-cpu flushes are, and whether global or not.
ppc and ppc64 have already found this issue, and worked around it by arranging
TLB flush from their ptep_test_and_clear_young: with the aid of pgtable rmap
pointers. I'm hoping ptep_clear_flush_young will allow ppc and ppc64 to
remove that special code, but won't change them myself.
It's worth noting that it is Andrea's anon_vma rmap which makes the vma
available for ptep_clear_flush_young in page_referenced_one: anonmm and
pte_chains would both need an additional find_vma for that.
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
25-akpm/mm/rmap.c | 6 +++---
1 files changed, 3 insertions(+), 3 deletions(-)
diff -puN mm/rmap.c~mm-flush-tlb-when-clearing-young mm/rmap.c
--- 25/mm/rmap.c~mm-flush-tlb-when-clearing-young Wed Jun 2 15:12:30 2004
+++ 25-akpm/mm/rmap.c Wed Jun 2 15:12:30 2004
@@ -226,7 +226,7 @@ static int page_referenced_one(struct pa
if (page_to_pfn(page) != pte_pfn(*pte))
goto out_unmap;
- if (ptep_test_and_clear_young(pte))
+ if (ptep_clear_flush_young(vma, address, pte))
referenced++;
(*mapcount)--;
@@ -465,7 +465,7 @@ static int try_to_unmap_one(struct page
* skipped over this mm) then we should reactivate it.
*/
if ((vma->vm_flags & (VM_LOCKED|VM_RESERVED)) ||
- ptep_test_and_clear_young(pte)) {
+ ptep_clear_flush_young(vma, address, pte)) {
ret = SWAP_FAIL;
goto out_unmap;
}
@@ -592,7 +592,7 @@ static int try_to_unmap_cluster(unsigned
if (PageReserved(page))
continue;
- if (ptep_test_and_clear_young(pte))
+ if (ptep_clear_flush_young(vma, address, pte))
continue;
/* Nuke the page table entry. */
_