Thank you for proposing a patch.
On 2018/09/10 21:55, Michal Hocko wrote:
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 5f2b2b1..99bb9ce 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -3091,7 +3081,31 @@ void exit_mmap(struct mm_struct *mm)
> /* update_hiwater_rss(mm) here? but nobody should be looking */
> /* Use -1 here to ensure all VMAs in the mm are unmapped */
> unmap_vmas(&tlb, vma, 0, -1);
unmap_vmas() might involve hugepage path. Is it safe to race with the OOM reaper?
i_mmap_lock_write(vma->vm_file->f_mapping);
__unmap_hugepage_range_final(tlb, vma, start, end, NULL);
i_mmap_unlock_write(vma->vm_file->f_mapping);
> - free_pgtables(&tlb, vma, FIRST_USER_ADDRESS, USER_PGTABLES_CEILING);
> +
> + /* oom_reaper cannot race with the page tables teardown */
> + if (oom)
> + down_write(&mm->mmap_sem);
> + /*
> + * Hide vma from rmap and truncate_pagecache before freeing
> + * pgtables
> + */
> + while (vma) {
> + unlink_anon_vmas(vma);
> + unlink_file_vma(vma);
> + vma = vma->vm_next;
> + }
> + vma = mm->mmap;
> + if (oom) {
> + /*
> + * the exit path is guaranteed to finish without any unbound
> + * blocking at this stage so make it clear to the caller.
> + */
> + mm->mmap = NULL;
> + up_write(&mm->mmap_sem);
> + }
> +
> + free_pgd_range(&tlb, vma->vm_start, vma->vm_prev->vm_end,
> + FIRST_USER_ADDRESS, USER_PGTABLES_CEILING);
Are you trying to inline free_pgtables() here? But some architectures are
using hugetlb_free_pgd_range() which does more than free_pgd_range(). Are
they really safe (with regard to memory allocation dependency and flags
manipulation) ?
> tlb_finish_mmu(&tlb, 0, -1);
>
> /*
Also, how do you plan to give this thread enough CPU resources, for this thread might
be SCHED_IDLE priority? Since this thread might not be a thread which is exiting
(because this is merely a thread which invoked __mmput()), we can't use boosting
approach. CPU resource might be given eventually unless schedule_timeout_*() is used,
but it might be deadly slow if allocating threads keep wasting CPU resources.
Also, why MMF_OOM_SKIP will not be set if the OOM reaper handed over?
