memcgroup: tidy up mem_cgroup_charge_common

Tidy up mem_cgroup_charge_common before extending it.  Adjust some comments,
but mainly clean up its loop: I've an aversion to loops full of continues,
then a break or a goto at the bottom.  And the is_atomic test should be on the
__GFP_WAIT bit, not GFP_ATOMIC bits.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 15 insertions, 29 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 160101a05b4d..dbf571547c03 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -345,23 +345,22 @@ retry:
                         goto done;
                 }
         }
-
         unlock_page_cgroup(page);
 
         pc = kzalloc(sizeof(struct page_cgroup), gfp_mask);
         if (pc == NULL)
                 goto err;
 
-        rcu_read_lock();
         /*
-         * We always charge the cgroup the mm_struct belongs to
-         * the mm_struct's mem_cgroup changes on task migration if the
+         * We always charge the cgroup the mm_struct belongs to.
+         * The mm_struct's mem_cgroup changes on task migration if the
          * thread group leader migrates. It's possible that mm is not
          * set, if so charge the init_mm (happens for pagecache usage).
          */
         if (!mm)
                 mm = &init_mm;
 
+        rcu_read_lock();
         mem = rcu_dereference(mm->mem_cgroup);
         /*
          * For every charge from the cgroup, increment reference
@@ -375,12 +374,8 @@ retry:
          * the cgroup limit.
          */
         while (res_counter_charge(&mem->res, PAGE_SIZE)) {
-                bool is_atomic = gfp_mask & GFP_ATOMIC;
-                /*
-                 * We cannot reclaim under GFP_ATOMIC, fail the charge
-                 */
-                if (is_atomic)
-                        goto noreclaim;
+                if (!(gfp_mask & __GFP_WAIT))
+                        goto out;
 
                 if (try_to_free_mem_cgroup_pages(mem, gfp_mask))
                         continue;
@@ -394,23 +389,12 @@ retry:
                  */
                 if (res_counter_check_under_limit(&mem->res))
                         continue;
-                        /*
-                         * Since we control both RSS and cache, we end up with a
-                         * very interesting scenario where we end up reclaiming
-                         * memory (essentially RSS), since the memory is pushed
-                         * to swap cache, we eventually end up adding those
-                         * pages back to our list. Hence we give ourselves a
-                         * few chances before we fail
-                         */
-                else if (nr_retries--) {
-                        congestion_wait(WRITE, HZ/10);
-                        continue;
+
+                if (!nr_retries--) {
+                        mem_cgroup_out_of_memory(mem, gfp_mask);
+                        goto out;
                 }
-noreclaim:
-                css_put(&mem->css);
-                if (!is_atomic)
-                        mem_cgroup_out_of_memory(mem, GFP_KERNEL);
-                goto free_pc;
+                congestion_wait(WRITE, HZ/10);
         }
 
         atomic_set(&pc->ref_cnt, 1);
@@ -419,10 +403,11 @@ noreclaim:
         pc->flags = 0;
         if (ctype == MEM_CGROUP_CHARGE_TYPE_CACHE)
                 pc->flags |= PAGE_CGROUP_FLAG_CACHE;
+
         if (page_cgroup_assign_new_page_cgroup(page, pc)) {
                 /*
-                 * an another charge is added to this page already.
-                 * we do take lock_page_cgroup(page) again and read
+                 * Another charge has been added to this page already.
+                 * We take lock_page_cgroup(page) again and read
                  * page->cgroup, increment refcnt.... just retry is OK.
                  */
                 res_counter_uncharge(&mem->res, PAGE_SIZE);
@@ -437,7 +422,8 @@ noreclaim:
 
 done:
         return 0;
-free_pc:
+out:
+        css_put(&mem->css);
         kfree(pc);
 err:
         return -ENOMEM;