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authorMichal Hocko <mhocko@suse.com>2018-08-21 21:52:37 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2018-08-22 10:52:44 -0700
commitaf5679fbc669f31f7ebd0d473bca76c24c07de30 (patch)
tree1c7578d9acafeca6866110546819eab839c749c1 /mm
parent93065ac753e4443840a057bfef4be71ec766fde9 (diff)
downloadlinux-stericsson-af5679fbc669f31f7ebd0d473bca76c24c07de30.tar.gz
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@kernel.org: oom_reap_task_mm should return false when __oom_reap_task_mm did] Link: http://lkml.kernel.org/r/20180724141747.GP28386@dhcp22.suse.cz Link: http://lkml.kernel.org/r/20180719075922.13784-1-mhocko@kernel.org Signed-off-by: Michal Hocko <mhocko@suse.com> Suggested-by: David Rientjes <rientjes@google.com> Acked-by: David Rientjes <rientjes@google.com> Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/mmap.c2
-rw-r--r--mm/oom_kill.c30
2 files changed, 4 insertions, 28 deletions
diff --git a/mm/mmap.c b/mm/mmap.c
index bb2a7e097c7d..5f2b2b184c60 100644
--- a/mm/mmap.c
+++ b/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 --git a/mm/oom_kill.c b/mm/oom_kill.c
index be31a1e0fe78..66a86dd049a0 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -535,28 +535,9 @@ bool __oom_reap_task_mm(struct mm_struct *mm)
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_struct *tsk, struct mm_struct *mm)
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_struct *tsk, struct mm_struct *mm)
/* 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_struct *tsk, struct mm_struct *mm)
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