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VS0Dc298b8XmEThvh4m1SmnZ5GXVWeyvzz+XxqvadK995s+trZPMNfOVXs84UNkBNBaloZTFfZiyYKpejrAgwI47O0vwGKodmcy0ELoFYrKep6k+3h7kSkRHn359EEfjhRYZJo2frGo8A8GOa4w885KXEbkHRexz/J0aDjXl/J0MabeShForjgQVp3dyEjUbK+QMk6Ek6ljQVD6dJB1n1jq4MJk+PQoYk79U2me7J0vgztufAAlUYa7N2v/e9bC1/122Ch3q7xq5bYxBl8U1cv9Izm6cMOoXgQAK3jvwRcw2mqeuqYBDh/54DrI+JhybzR0V0YEd8Fh43dAaifIqtfWksOA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 5/1/24 11:56 PM, David Hildenbrand wrote: > On 02.05.24 03:05, Alistair Popple wrote: >> Jason Gunthorpe writes: ... >>>> This doesn't make sense.  IFF a blind retry is all that is needed it >>>> should be done in the core functionality.  I fear it's not that easy, >>>> though. >>> >>> +1 >>> >>> This migration retry weirdness is a GUP issue, it needs to be solved >>> in the mm not exposed to every pin_user_pages caller. >>> >>> If it turns out ZONE_MOVEABLE pages can't actually be reliably moved >>> then it is pretty broken.. >> >> I wonder if we should remove the arbitrary retry limit in >> migrate_pages() entirely for ZONE_MOVEABLE pages and just loop until >> they migrate? By definition there should only be transient references on >> these pages so why do we need to limit the number of retries in the >> first place? > > There are some weird things that still needs fixing: vmsplice() is the > example that doesn't use FOLL_LONGTERM. > Hi David! Do you have any other call sites in mind? It sounds like one way forward is to fix each call site... This is an unhappy story right now: the pin_user_pages*() APIs are significantly worse than before the "migrate pages away automatically" upgrade, from a user point of view. Because now, the APIs fail intermittently for callers who follow the rules--because pin_user_pages() is not fully working yet, basically. Other ideas, large or small, about how to approach a fix? thanks, -- John Hubbard NVIDIA