> On Jan 20, 2022, at 10:00 AM, David Hildenbrand <david@xxxxxxxxxx> wrote: > > On 20.01.22 18:48, Nadav Amit wrote: >> >>> On Jan 20, 2022, at 6:15 AM, David Hildenbrand <david@xxxxxxxxxx> wrote: >>> >>> On 17.01.22 14:31, zhangliang (AG) wrote: >>>> Sure, I will do that :) >>> >>> I'm polishing up / testing the patches and might send something out for discussion shortly. >>> Just a note that on my branch was a version with a wrong condition that should have been fixed now. >>> >> >> Sorry for being late for the discussion. >> >> David, does any of it regards the lru_cache_add() reference issue that I >> mentioned? [1] > > No, unfortunately not in that part of my work. *Maybe* we could also try > to handle that reference similarly to the swapcache, but the question is > if we can't wait for PageAnonExclusive. > > Right now I have the following in mind to get most parts working as > exptected: > > 1. Optimize reuse logic for the swapcache as it seems to be easy > 2. Streamline COW logic and remove reuse_swap_page() -- fix the CVE for > THP. > 3. Introduce PageAnonExclusive and allow FOLL_PIN only on > PageAnonExclusive pages. > 4. Convert O_DIRECT to FOLL_PIN > > We will never ever have to copy a page PageAnonExclusive page in the COW > handler and can immediately reuse it without even locking the page. The > existing reuse logic is essentially then used to reset PageAnonExclusive > on a page (thus it makes sense to work on it) where the flag is not set > anymore -- or on a fresh page if we have to copy. > > That implies that all these additional references won't care if your app > doesn't fork() or KSM isn't active. Consequently, anything that > read-protects anonymous pages will work as expected and should be as > fast as it gets. > > Sounds good? At least to me. If only swap/migration entries wouldn't be > harder to handle than I'd wish, that's why it's taking a little and will > take a little longer. Thanks for the quick response. I would have to see the logic to set/clear PageAnonExclusive to fully understand how things are handled. BTW, I just saw this patch form PeterZ [1] that seems to be related, as it deals with changing protection on pinned pages. [1] https://lore.kernel.org/linux-mm/20220120160822.666778608@xxxxxxxxxxxxx/
