The patch titled
Subject: mm, oom: remove oom_lock from oom_reaper
has been removed from the -mm tree. Its filename was
mm-oom-remove-oom_lock-from-oom_reaper.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
From: Michal Hocko <mhocko@xxxxxxxx>
Subject: mm, oom: remove oom_lock from oom_reaper
oom_reaper used to rely on the oom_lock since e2fe14564d33 ("oom_reaper:
close race with exiting task"). We do not really need the lock anymore
though. 212925802454 ("mm: oom: let oom_reap_task and exit_mmap run
concurrently") has removed serialization with the exit path based on the
mm reference count and so we do not really rely on the oom_lock anymore.
Tetsuo was arguing that at least MMF_OOM_SKIP should be set under the lock
to prevent from races when the page allocator didn't manage to get the
freed (reaped) memory in __alloc_pages_may_oom but it sees the flag later
on and move on to another victim. Although this is possible in principle
let's wait for it to actually happen in real life before we make the
locking more complex again.
Therefore remove the oom_lock for oom_reaper paths (both exit_mmap and
oom_reap_task_mm). The reaper serializes with exit_mmap by mmap_sem +
MMF_OOM_SKIP flag. There is no synchronization with out_of_memory path
now.
[mhocko@xxxxxxxxxx: oom_reap_task_mm should return false when __oom_reap_task_mm did]
Link: http://lkml.kernel.org/r/20180724141747.GP28386@xxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/20180719075922.13784-1-mhocko@xxxxxxxxxx
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
Suggested-by: David Rientjes <rientjes@xxxxxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
diff -puN mm/mmap.c~mm-oom-remove-oom_lock-from-oom_reaper mm/mmap.c
--- a/mm/mmap.c~mm-oom-remove-oom_lock-from-oom_reaper
+++ a/mm/mmap.c
@@ -3063,9 +3063,7 @@ void exit_mmap(struct mm_struct *mm)
* which clears VM_LOCKED, otherwise the oom reaper cannot
* reliably test it.
*/
- mutex_lock(&oom_lock);
(void)__oom_reap_task_mm(mm);
- mutex_unlock(&oom_lock);
set_bit(MMF_OOM_SKIP, &mm->flags);
down_write(&mm->mmap_sem);
diff -puN mm/oom_kill.c~mm-oom-remove-oom_lock-from-oom_reaper mm/oom_kill.c
--- a/mm/oom_kill.c~mm-oom-remove-oom_lock-from-oom_reaper
+++ a/mm/oom_kill.c
@@ -535,28 +535,9 @@ bool __oom_reap_task_mm(struct mm_struct
static bool oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
{
- bool ret = true;
-
- /*
- * We have to make sure to not race with the victim exit path
- * and cause premature new oom victim selection:
- * oom_reap_task_mm exit_mm
- * mmget_not_zero
- * mmput
- * atomic_dec_and_test
- * exit_oom_victim
- * [...]
- * out_of_memory
- * select_bad_process
- * # no TIF_MEMDIE task selects new victim
- * unmap_page_range # frees some memory
- */
- mutex_lock(&oom_lock);
-
if (!down_read_trylock(&mm->mmap_sem)) {
- ret = false;
trace_skip_task_reaping(tsk->pid);
- goto unlock_oom;
+ return false;
}
/*
@@ -568,7 +549,7 @@ static bool oom_reap_task_mm(struct task
if (test_bit(MMF_OOM_SKIP, &mm->flags)) {
up_read(&mm->mmap_sem);
trace_skip_task_reaping(tsk->pid);
- goto unlock_oom;
+ return true;
}
trace_start_task_reaping(tsk->pid);
@@ -576,8 +557,7 @@ static bool oom_reap_task_mm(struct task
/* failed to reap part of the address space. Try again later */
if (!__oom_reap_task_mm(mm)) {
up_read(&mm->mmap_sem);
- ret = false;
- goto unlock_oom;
+ return false;
}
pr_info("oom_reaper: reaped process %d (%s), now anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n",
@@ -588,9 +568,7 @@ static bool oom_reap_task_mm(struct task
up_read(&mm->mmap_sem);
trace_finish_task_reaping(tsk->pid);
-unlock_oom:
- mutex_unlock(&oom_lock);
- return ret;
+ return true;
}
#define MAX_OOM_REAP_RETRIES 10
_
Patches currently in -mm which might be from mhocko@xxxxxxxx are
