Commit 212925802454672e ("mm: oom: let oom_reap_task and exit_mmap run
concurrently") moved the location of setting MMF_OOM_SKIP from __mmput()
in kernel/fork.c (which is used by both MMU and !MMU) to exit_mm() in
mm/mmap.c (which is used by MMU only). As a result, that commit required
OOM victims in !MMU kernels to disappear from the task list in order to
reenable the OOM killer, for !MMU kernels can no longer set MMF_OOM_SKIP
(unless the OOM victim's mm is shared with global init process).
While it would be possible to restore MMF_OOM_SKIP in __mmput() for !MMU
kernels, let's forget about possibility of OOM livelock for !MMU kernels
caused by failing to set MMF_OOM_SKIP, by setting MMF_OOM_SKIP at
oom_kill_process(), for the invocation of the OOM killer is a rare event
for !MMU systems from the beginning. By doing so, we can get rid of
special treatment for !MMU case in commit cd04ae1e2dc8e365 ("mm, oom:
do not rely on TIF_MEMDIE for memory reserves access"). And "mm,oom:
Use ALLOC_OOM for OOM victim's last second allocation." will allow the
OOM victim to try ALLOC_OOM (instead of ALLOC_NO_WATERMARKS) allocation
before killing more OOM victims.
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
---
mm/internal.h | 9 ---------
mm/oom_kill.c | 7 +++++--
mm/page_alloc.c | 12 +-----------
3 files changed, 6 insertions(+), 22 deletions(-)
diff --git a/mm/internal.h b/mm/internal.h
index e6bd351..f0eb8d90 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -481,16 +481,7 @@ unsigned long reclaim_clean_pages_from_list(struct zone *zone,
/* Mask to get the watermark bits */
#define ALLOC_WMARK_MASK (ALLOC_NO_WATERMARKS-1)
-/*
- * Only MMU archs have async oom victim reclaim - aka oom_reaper so we
- * cannot assume a reduced access to memory reserves is sufficient for
- * !MMU
- */
-#ifdef CONFIG_MMU
#define ALLOC_OOM 0x08
-#else
-#define ALLOC_OOM ALLOC_NO_WATERMARKS
-#endif
#define ALLOC_HARDER 0x10 /* try to alloc harder */
#define ALLOC_HIGH 0x20 /* __GFP_HIGH set */
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 6949465..d57dcd5 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -647,6 +647,8 @@ static int __init oom_init(void)
#else
static inline void wake_oom_reaper(struct task_struct *tsk)
{
+ /* tsk->mm != NULL because tsk == current or task_lock is held. */
+ set_bit(MMF_OOM_SKIP, &tsk->mm->flags);
}
#endif /* CONFIG_MMU */
@@ -829,7 +831,7 @@ static void oom_kill_process(struct oom_control *oc, const char *message)
unsigned int victim_points = 0;
static DEFINE_RATELIMIT_STATE(oom_rs, DEFAULT_RATELIMIT_INTERVAL,
DEFAULT_RATELIMIT_BURST);
- bool can_oom_reap = true;
+ bool can_oom_reap = IS_ENABLED(CONFIG_MMU);
/*
* If the task is already exiting, don't alarm the sysadmin or kill
@@ -929,7 +931,6 @@ static void oom_kill_process(struct oom_control *oc, const char *message)
continue;
if (is_global_init(p)) {
can_oom_reap = false;
- set_bit(MMF_OOM_SKIP, &mm->flags);
pr_info("oom killer %d (%s) has mm pinned by %d (%s)\n",
task_pid_nr(victim), victim->comm,
task_pid_nr(p), p->comm);
@@ -947,6 +948,8 @@ static void oom_kill_process(struct oom_control *oc, const char *message)
if (can_oom_reap)
wake_oom_reaper(victim);
+ else
+ set_bit(MMF_OOM_SKIP, &mm->flags);
mmdrop(mm);
put_task_struct(victim);
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index fbbc95a..ff435f7 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3711,17 +3711,7 @@ static void wake_all_kswapds(unsigned int order, const struct alloc_context *ac)
static bool oom_reserves_allowed(struct task_struct *tsk)
{
- if (!tsk_is_oom_victim(tsk))
- return false;
-
- /*
- * !MMU doesn't have oom reaper so give access to memory reserves
- * only to the thread with TIF_MEMDIE set
- */
- if (!IS_ENABLED(CONFIG_MMU) && !test_thread_flag(TIF_MEMDIE))
- return false;
-
- return true;
+ return tsk_is_oom_victim(tsk);
}
/*
--
1.8.3.1
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