[Devel] [PATCH rh7 3/6] oom: drop OOM_SCAN_ABORT

[Vladimir Davydov]

From: Vladimir Davydov <vdavydov at parallels.com>

Patchset description: oom enhancements - part 2

 - Patches 1-2 prepare memcg for upcoming changes in oom design.
 - Patch 3 reworks oom locking design so that the executioner waits for
   victim to exit. This is necessary to increase oom kill rate, which is
   essential for berserker mode.
 - Patch 4 drops unused OOM_SCAN_ABORT
 - Patch 5 introduces oom timeout.
   https://jira.sw.ru/browse/PSBM-38581
 - Patch 6 makes oom fairer when it comes to selecting a victim among
   different containers.
   https://jira.sw.ru/browse/PSBM-37915
 - Patch 7 prepares oom for introducing berserker mode
 - Patch 8 resurrects oom berserker mode, which is supposed to cope with
   actively forking processes.
   https://jira.sw.ru/browse/PSBM-17930

https://jira.sw.ru/browse/PSBM-26973

Changes in v3:
 - rework oom_trylock (patch 3)
 - select exiting process instead of aborting oom scan so as not to keep
   busy-waiting for an exiting process to exit (patches 3, 4)
 - cleanup oom timeout handling + fix stuck process trace dumped
   multiple times on timeout (patch 5)
 - set max_overdraft to ULONG_MAX on selected processes (patch 6)
 - rework oom berserker process selection logic (patches 7, 8)

Changes in v2:
 - s/time_after/time_after_eq to avoid BUG_ON in oom_trylock (patch 4)
 - propagate victim to the context that initiated oom in oom_unlock
   (patch 6)
 - always set oom_end on releasing oom context (patch 6)

Vladimir Davydov (8):
  memcg: add mem_cgroup_get/put helpers
  memcg: add lock for protecting memcg->oom_notify list
  oom: rework locking design
  oom: introduce oom timeout
  oom: drop OOM_SCAN_ABORT
  oom: rework logic behind memory.oom_guarantee
  oom: pass points and overdraft to oom_kill_process
  oom: resurrect berserker mode

Reviewed-by: Kirill Tkhai <ktkhai at odin.com>

=========================================
This patch description:

It is not used anymore, neither should it be used with the new locking
design.

Signed-off-by: Vladimir Davydov <vdavydov at parallels.com>
---
 include/linux/oom.h | 1 -
 mm/memcontrol.c     | 6 ------
 mm/oom_kill.c       | 7 +------
 3 files changed, 1 insertion(+), 13 deletions(-)

diff --git a/include/linux/oom.h b/include/linux/oom.h
index f804551c0a5d..6d4a94f15f2a 100644
--- a/include/linux/oom.h
+++ b/include/linux/oom.h
@@ -27,7 +27,6 @@ enum oom_constraint {
 enum oom_scan_t {
 	OOM_SCAN_OK,		/* scan thread and find its badness */
 	OOM_SCAN_CONTINUE,	/* do not consider thread for oom kill */
-	OOM_SCAN_ABORT,		/* abort the iteration and return */
 	OOM_SCAN_SELECT,	/* always select this thread first */
 };
 
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 7ff7633d185a..6d79d961fd3e 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2065,12 +2065,6 @@ retry:
 				/* fall through */
 			case OOM_SCAN_CONTINUE:
 				continue;
-			case OOM_SCAN_ABORT:
-				cgroup_iter_end(cgroup, &it);
-				mem_cgroup_iter_break(memcg, iter);
-				if (chosen)
-					put_task_struct(chosen);
-				return;
 			case OOM_SCAN_OK:
 				break;
 			};
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index fd6defa7c6de..36f6454daace 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -358,9 +358,6 @@ retry:
 			/* fall through */
 		case OOM_SCAN_CONTINUE:
 			continue;
-		case OOM_SCAN_ABORT:
-			rcu_read_unlock();
-			return ERR_PTR(-1UL);
 		case OOM_SCAN_OK:
 			break;
 		};
@@ -890,11 +887,9 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
 	if (!p) {
 		dump_header(NULL, gfp_mask, order, NULL, mpol_mask);
 		panic("Out of memory and no killable processes...\n");
-	}
-	if (PTR_ERR(p) != -1UL) {
+	} else
 		oom_kill_process(p, gfp_mask, order, points, totalpages, NULL,
 				 nodemask, "Out of memory");
-	}
 }
 
 /*
-- 
2.1.4