On Thu 02-06-22 13:31:27, Liam Howlett wrote:
> * Michal Hocko <mhocko@xxxxxxxx> [220602 02:53]:
> > On Wed 01-06-22 14:47:41, Suren Baghdasaryan wrote:
> > > On Wed, Jun 1, 2022 at 2:36 PM Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> > [...]
> > > > But iirc mapletree wants to retain a write_lock here, so I ended up with
> > > >
> > > > void exit_mmap(struct mm_struct *mm)
> > > > {
> > > > struct mmu_gather tlb;
> > > > struct vm_area_struct *vma;
> > > > unsigned long nr_accounted = 0;
> > > > MA_STATE(mas, &mm->mm_mt, 0, 0);
> > > > int count = 0;
> > > >
> > > > /* mm's last user has gone, and its about to be pulled down */
> > > > mmu_notifier_release(mm);
> > > >
> > > > mmap_write_lock(mm);
> > > > arch_exit_mmap(mm);
> > > >
> > > > vma = mas_find(&mas, ULONG_MAX);
> > > > if (!vma) {
> > > > /* Can happen if dup_mmap() received an OOM */
> > > > mmap_write_unlock(mm);
> > > > return;
> > > > }
> > > >
> > > > lru_add_drain();
> > > > flush_cache_mm(mm);
> > > > tlb_gather_mmu_fullmm(&tlb, mm);
> > > > /* update_hiwater_rss(mm) here? but nobody should be looking */
> > > > /* Use ULONG_MAX here to ensure all VMAs in the mm are unmapped */
> > > > unmap_vmas(&tlb, &mm->mm_mt, vma, 0, ULONG_MAX);
> > > >
> > > > /*
> > > > * Set MMF_OOM_SKIP to hide this task from the oom killer/reaper
> > > > * because the memory has been already freed. Do not bother checking
> > > > * mm_is_oom_victim because setting a bit unconditionally is cheaper.
> > > > */
> > > > set_bit(MMF_OOM_SKIP, &mm->flags);
> > > > free_pgtables(&tlb, &mm->mm_mt, vma, FIRST_USER_ADDRESS,
> > > > USER_PGTABLES_CEILING);
> > > > tlb_finish_mmu(&tlb);
> > > >
> > > > /*
> > > > * Walk the list again, actually closing and freeing it, with preemption
> > > > * enabled, without holding any MM locks besides the unreachable
> > > > * mmap_write_lock.
> > > > */
> > > > do {
> > > > if (vma->vm_flags & VM_ACCOUNT)
> > > > nr_accounted += vma_pages(vma);
> > > > remove_vma(vma);
> > > > count++;
> > > > cond_resched();
> > > > } while ((vma = mas_find(&mas, ULONG_MAX)) != NULL);
> > > >
> > > > BUG_ON(count != mm->map_count);
> > > >
> > > > trace_exit_mmap(mm);
> > > > __mt_destroy(&mm->mm_mt);
> > > > mm->mmap = NULL;
> > >
> > > ^^^ this line above needs to be removed when the patch is applied over
> > > the maple tree patchset.
> >
> > I am not fully up to date on the maple tree changes. Could you explain
> > why resetting mm->mmap is not needed anymore please?
>
> The maple tree patch set removes the linked list, including mm->mmap.
> The call to __mt_destroy() means none of the old VMAs can be found in
> the race condition that mm->mmap = NULL was solving.
Thanks for the clarification, Liam.
--
Michal Hocko
SUSE Labs
