David Rientjes wrote:
> On Tue, 5 Dec 2017, David Rientjes wrote:
>
> > One way to solve the issue is to have two mm flags: one to indicate the mm
> > is entering unmap_vmas(): set the flag, do down_write(&mm->mmap_sem);
> > up_write(&mm->mmap_sem), then unmap_vmas(). The oom reaper needs this
> > flag clear, not MMF_OOM_SKIP, while holding down_read(&mm->mmap_sem) to be
> > allowed to call unmap_page_range(). The oom killer will still defer
> > selecting this victim for MMF_OOM_SKIP after unmap_vmas() returns.
> >
> > The result of that change would be that we do not oom reap from any mm
> > entering unmap_vmas(): we let unmap_vmas() do the work itself and avoid
> > racing with it.
> >
>
> I think we need something like the following?
This patch does not work. __oom_reap_task_mm() can find MMF_REAPING and
return true and sets MMF_OOM_SKIP before exit_mmap() calls down_write().
Also, I don't know what exit_mmap() is doing but I think that there is a
possibility that the OOM reaper tries to reclaim mlocked pages as soon as
exit_mmap() cleared VM_LOCKED flag by calling munlock_vma_pages_all().
if (mm->locked_vm) {
vma = mm->mmap;
while (vma) {
if (vma->vm_flags & VM_LOCKED)
munlock_vma_pages_all(vma);
vma = vma->vm_next;
}
}
/*
* munlock_vma_pages_range() - munlock all pages in the vma range.'
* @vma - vma containing range to be munlock()ed.
* @start - start address in @vma of the range
* @end - end of range in @vma.
*
* For mremap(), munmap() and exit().
*
* Called with @vma VM_LOCKED.
*
* Returns with VM_LOCKED cleared. Callers must be prepared to
* deal with this.
*
* We don't save and restore VM_LOCKED here because pages are
* still on lru. In unmap path, pages might be scanned by reclaim
* and re-mlocked by try_to_{munlock|unmap} before we unmap and
* free them. This will result in freeing mlocked pages.
*/
void munlock_vma_pages_range(struct vm_area_struct *vma,
unsigned long start, unsigned long end)
{
vma->vm_flags &= VM_LOCKED_CLEAR_MASK;
while (start < end) {
/*
* Things for munlock() are done here. But at this point,
* __oom_reap_task_mm() can call unmap_page_range() because
* can_madv_dontneed_vma() returns true due to VM_LOCKED
* being already cleared and MMF_OOM_SKIP is not yet set.
*/
}
}
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
