diff options
| -rw-r--r-- | mm/mlock.c | 41 |
1 files changed, 19 insertions, 22 deletions
diff --git a/mm/mlock.c b/mm/mlock.c index adcbe9032b5..2b8335a8940 100644 --- a/mm/mlock.c +++ b/mm/mlock.c @@ -88,23 +88,20 @@ void mlock_vma_page(struct page *page) } } -/* - * called from munlock()/munmap() path with page supposedly on the LRU. +/** + * munlock_vma_page - munlock a vma page + * @page - page to be unlocked * - * Note: unlike mlock_vma_page(), we can't just clear the PageMlocked - * [in try_to_munlock()] and then attempt to isolate the page. We must - * isolate the page to keep others from messing with its unevictable - * and mlocked state while trying to munlock. However, we pre-clear the - * mlocked state anyway as we might lose the isolation race and we might - * not get another chance to clear PageMlocked. If we successfully - * isolate the page and try_to_munlock() detects other VM_LOCKED vmas - * mapping the page, it will restore the PageMlocked state, unless the page - * is mapped in a non-linear vma. So, we go ahead and ClearPageMlocked(), - * perhaps redundantly. - * If we lose the isolation race, and the page is mapped by other VM_LOCKED - * vmas, we'll detect this in vmscan--via try_to_munlock() or try_to_unmap() - * either of which will restore the PageMlocked state by calling - * mlock_vma_page() above, if it can grab the vma's mmap sem. + * called from munlock()/munmap() path with page supposedly on the LRU. + * When we munlock a page, because the vma where we found the page is being + * munlock()ed or munmap()ed, we want to check whether other vmas hold the + * page locked so that we can leave it on the unevictable lru list and not + * bother vmscan with it. However, to walk the page's rmap list in + * try_to_munlock() we must isolate the page from the LRU. If some other + * task has removed the page from the LRU, we won't be able to do that. + * So we clear the PageMlocked as we might not get another chance. If we + * can't isolate the page, we leave it for putback_lru_page() and vmscan + * [page_referenced()/try_to_unmap()] to deal with. */ void munlock_vma_page(struct page *page) { @@ -123,12 +120,12 @@ void munlock_vma_page(struct page *page) putback_lru_page(page); } else { /* - * We lost the race. let try_to_unmap() deal - * with it. At least we get the page state and - * mlock stats right. However, page is still on - * the noreclaim list. We'll fix that up when - * the page is eventually freed or we scan the - * noreclaim list. + * Some other task has removed the page from the LRU. + * putback_lru_page() will take care of removing the + * page from the unevictable list, if necessary. + * vmscan [page_referenced()] will move the page back + * to the unevictable list if some other vma has it + * mlocked. */ if (PageUnevictable(page)) count_vm_event(UNEVICTABLE_PGSTRANDED); |