ksm: mem cgroup charge swapin copy

But ksm swapping does require one small change in mem cgroup handling. When do_swap_page()'s call to ksm_might_need_to_copy() does indeed substitute a duplicate page to accommodate a different anon_vma (or a the !PageSwapCache check in mem_cgroup_try_charge_swapin(). That was returning success without charging, on the assumption that pte_same() would fail after, which is not the case here. Originally I proposed that success, so that an unshrinkable mem cgroup at its limit would not fail unnecessarily; but that's a minor point, and there are plenty of other places where we may fail an overallocation which might later prove unnecessary. So just go ahead and do what all the other exceptions do: proceed to charge current mm. Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk> Cc: Izik Eidus <ieidus@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Chris Wright <chrisw@redhat.com> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

ksm: mem cgroup charge swapin copy
But ksm swapping does require one small change in mem cgroup handling. When do_swap_page()'s call to ksm_might_need_to_copy() does indeed substitute a duplicate page to accommodate a different anon_vma (or a the !PageSwapCache check in mem_cgroup_try_charge_swapin(). That was returning success without charging, on the assumption that pte_same() would fail after, which is not the case here. Originally I proposed that success, so that an unshrinkable mem cgroup at its limit would not fail unnecessarily; but that's a minor point, and there are plenty of other places where we may fail an overallocation which might later prove unnecessary. So just go ahead and do what all the other exceptions do: proceed to charge current mm. Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk> Cc: Izik Eidus <ieidus@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Chris Wright <chrisw@redhat.com> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Hugh Dickins · Linus Torvalds
1 parent 80e1482260
Showing 1 changed file with 4 additions and 3 deletions Side-by-side Diff
mm/memcontrol.c
@@ -1737,11 +1737,12 @@
 		goto charge_cur_mm;
 	/*
 	 * A racing thread's fault, or swapoff, may have already updated
-	 * the pte, and even removed page from swap cache: return success
-	 * to go on to do_swap_page()'s pte_same() test, which should fail.
+	 * the pte, and even removed page from swap cache: in those cases
+	 * do_swap_page()'s pte_same() test will fail; but there's also a
+	 * KSM case which does need to charge the page.
 	 */
 	if (!PageSwapCache(page))
-		return 0;
+		goto charge_cur_mm;
 	mem = try_get_mem_cgroup_from_swapcache(page);
 	if (!mem)
 		goto charge_cur_mm;
...	...	@@ -1737,11 +1737,12 @@
1737	1737	goto charge_cur_mm;
1738	1738	/*
1739	1739	* A racing thread's fault, or swapoff, may have already updated
1740		- * the pte, and even removed page from swap cache: return success
1741		- * to go on to do_swap_page()'s pte_same() test, which should fail.
	1740	+ * the pte, and even removed page from swap cache: in those cases
	1741	+ * do_swap_page()'s pte_same() test will fail; but there's also a
	1742	+ * KSM case which does need to charge the page.
1742	1743	*/
1743	1744	if (!PageSwapCache(page))
1744		- return 0;
	1745	+ goto charge_cur_mm;
1745	1746	mem = try_get_mem_cgroup_from_swapcache(page);
1746	1747	if (!mem)
1747	1748	goto charge_cur_mm;