On 2021/7/13 21:34, Matthew Wilcox wrote: > On Tue, Jul 13, 2021 at 09:13:51PM +0800, Miaohe Lin wrote: >>>> When the MADV_FREE pages are redirtied before they could be reclaimed, the pages >>>> should be put back to anonymous LRU list by setting SwapBacked flag, thus the >>>> pages will be reclaimed in normal swapout way. >>> >>> Agreed. But the question is why this needs an explicit handling here >>> when we already do handle this case when trying to unmap the page. >> >> This makes me think more. It seems even the page_ref_freeze call is guaranteed to >> success as no one can grab the page refcnt after the page is successfully unmapped. > > NO! This is wrong. Every page can have its refcount speculatively raised > (and then lowered). The two prime candidates for this are lockless GUP > and page cache lookups, but there can be others too. > Many thanks for pointing this out. My overlook! Sorry! So, it seems lockless GUP can redirty the MADV_FREE page. But is it ok to just release a redirtied MADV_FREE pages? Because we hold the last reference here and the page will be freed anyway... > . >
