On Thu, Dec 9, 2021 at 1:12 AM Michal Hocko <mhocko@xxxxxxxx> wrote: > > Do we want this on top? As we discussed in this thread https://lore.kernel.org/all/YY4snVzZZZYhbigV@xxxxxxxxxxxxxx, __oom_reap_task_mm in exit_mmap allows oom-reaper/process_mrelease to unmap pages in parallel with exit_mmap without blocking each other. Removal of __oom_reap_task_mm from exit_mmap prevents this parallelism and has a negative impact on performance. So the conclusion of that thread I thought was to keep that part. My understanding is that we also wanted to remove MMF_OOM_SKIP as a follow-up patch but __oom_reap_task_mm would stay. > ---- > From 58b04ae6dc97b0105ea2651daca55cf2386f69b4 Mon Sep 17 00:00:00 2001 > From: Michal Hocko <mhocko@xxxxxxxx> > Date: Thu, 9 Dec 2021 10:07:51 +0100 > Subject: [PATCH] mm: drop MMF_OOM_SKIP from exit_mmap > > MMF_OOM_SKIP used to play a synchronization role between exit_mmap and > oom repear in the past. Since the exclusive mmap_sem is held in > exit_mmap to cover all destructive operations the flag synchronization > is not needed anymore and we can safely drop it. Just make sure that > mm->mmap is set to NULL so that nobody will access the freed vma list. > > Signed-off-by: Michal Hocko <mhocko@xxxxxxxx> > --- > mm/mmap.c | 23 +---------------------- > 1 file changed, 1 insertion(+), 22 deletions(-) > > diff --git a/mm/mmap.c b/mm/mmap.c > index f4e09d390a07..0d6af9d89aa8 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -3129,28 +3129,6 @@ void exit_mmap(struct mm_struct *mm) > /* mm's last user has gone, and its about to be pulled down */ > mmu_notifier_release(mm); > > - if (unlikely(mm_is_oom_victim(mm))) { > - /* > - * Manually reap the mm to free as much memory as possible. > - * Then, as the oom reaper does, set MMF_OOM_SKIP to disregard > - * this mm from further consideration. Taking mm->mmap_lock for > - * write after setting MMF_OOM_SKIP will guarantee that the oom > - * reaper will not run on this mm again after mmap_lock is > - * dropped. > - * > - * Nothing can be holding mm->mmap_lock here and the above call > - * to mmu_notifier_release(mm) ensures mmu notifier callbacks in > - * __oom_reap_task_mm() will not block. > - * > - * This needs to be done before calling unlock_range(), > - * which clears VM_LOCKED, otherwise the oom reaper cannot > - * reliably test it. > - */ > - (void)__oom_reap_task_mm(mm); > - > - set_bit(MMF_OOM_SKIP, &mm->flags); > - } > - > mmap_write_lock(mm); > if (mm->locked_vm) > unlock_range(mm->mmap, ULONG_MAX); > @@ -3180,6 +3158,7 @@ void exit_mmap(struct mm_struct *mm) > vma = remove_vma(vma); > cond_resched(); > } > + mm->mmap = NULL; > mmap_write_unlock(mm); > vm_unacct_memory(nr_accounted); > } > -- > 2.30.2 > > -- > Michal Hocko > SUSE Labs
