On Thu 02-06-22 13:31:27, Liam Howlett wrote:
- Michal Hocko mhocko@suse.com [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@linux-foundation.org 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.