Messages in this thread | | | Date | Thu, 5 Feb 2009 08:35:43 +0900 | From | MinChan Kim <> | Subject | Re: [PATCH v2] fix mlocked page counter mistmatch |
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On Wed, Feb 04, 2009 at 07:28:19PM +0900, KOSAKI Motohiro wrote: > > With '29-rc3-git5', I found, > > > > static int try_to_mlock_page(struct page *page, struct vm_area_struct *vma) > > { > > int mlocked = 0; > > > > if (down_read_trylock(&vma->vm_mm->mmap_sem)) { > > if (vma->vm_flags & VM_LOCKED) { > > mlock_vma_page(page); > > mlocked++; /* really mlocked the page */ > > } > > up_read(&vma->vm_mm->mmap_sem); > > } > > return mlocked; > > } > > > > It still try to downgrade mmap_sem. > > Do I miss something ? > > sorry, I misunderstood your "downgrade". I said linus removed downgrade_write(&mma_sem). > > Now, I understand this issue perfectly. I agree you and lee-san's fix is correct. > Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Good. I will send adrew with your ACK agian.
> > > and, I think current try_to_mlock_page() is correct. no need change. > Why? > > 1. Generally, mmap_sem holding is necessary when vma->vm_flags accessed. > that's vma's basic rule. > 2. However, try_to_unmap_one() doesn't held mamp_sem. but that's ok. > it often get incorrect result. but caller consider incorrect value safe. > 3. try_to_mlock_page() need mmap_sem because it obey rule (1). > 4. in try_to_mlock_page(), if down_read_trylock() is failure, > we can't move the page to unevictable list. but that's ok. > the page in evictable list is periodically try to reclaim. and > be called try_to_unmap(). > try_to_unmap() (and its caller) also move the unevictable page to unevictable list. > Therefore, in long term view, the page leak is not happend.
Thanks for clarification. In long term view, you're right.
but My concern is that munlock[all] pathes always hold down of mmap_sem. After all, down_read_trylock always wil fail for such cases.
So, current task's mlocked pages only can be reclaimed by background or direct reclaim path if the task don't exit.
I think it can increase reclaim overhead unnecessary if there are lots of such tasks.
What's your opinion ?
> > this explanation is enough? > > thanks. >
-- Kinds Regards MinChan Kim
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