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U2FsdGVkX188XrlaXg6U74btfrZfs/axMmFkhIoOajQyAPVERMe2S216QF9DRUjlQ/1aCL6zifRAD8T+xP2/kQ6c6ThaD6N8tbBv/KeINiV8mAbQn2QYwwHaKzsU77SWb5FuMhZz3Vm0gaxUxpsyYqizFhjL3W7WPj/YThg4gcJMKyA6c7edIM2Lw/7MCJ5NHhIU0WJsjA2rWhC14iIiql6kM+En4w70giTN/qEwWe4XtMjdkIIbpUq/B//QIUlRUFW+NjrbGDgdbCL7sfq5DWlbtEyyjYWs48KDIa55eKHhLEdQqwFIA6XvWF8WZ1/jucdjRgKOwJmcUAy70xaZyw0J4DCW/KNezH7IYE7pNYnhoCEbsZzUph9xqf54tbum0Ca8/FzFWFGjtXWwL+w4RCwY6FqCvtNe4frtAVWdrlAx66hmOaJows/fkjAl5MZWIIF0WXGWZC7TVJ9HSxgB1FlRh9JzC79qUF22MMiD+p5ztv7Bx286PRKXsuGYIovQs3DsFGKl7WU1JIP1+eJLe5K2edCcj6OVY+to7L5NEvHdW6TcStKFd5XEvTJ1IKu6rz3ZB27mvO+1hxnM/3BhYRmBAGu9ovN9OxMDbHYtFaCGBIjNepyQItDg8PKTxeEFcVsb5+XDmeCMtiuw9mT+oeZ2bLpkWTuTEIKb5Sh5hkBex9Dgv0frkja32jiOROumQGYBrZfAM3rZyC4lxuBjuVQSPJ4GGhhkmN6VnoBDz38A1l7qH3dda3yWOVTdlZf8cdV119NoXdNpjaenyOtOFKaPGLr4PhbcGQYbYKYRNzfn/idkB3nUD0I5E2uyXlXxnVg41V51Vsi+00TTDoDdBdwl/Io5bb5jVaqEywKctsuJc3wswTaUU+QPZIGOr7SlqZaajV9UEhDLL5sCaDyp6VUOP8BZ+FofMGEtG1DBHGIYxmVSRrcpiC+Pmw105m+/JFLn13fXAGagvPdwy2K 3v+P4wJ7 /Va4d5rqhu7QRGdGr8oiROIsWf/vUh9L7/s7Tab6UtBvEKjuG7gfE4OvOJwOtsfe8/JTS 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 2026-02-02 at 20:13 +1100, Thomas Hellström wrote... > On Sat, 2026-01-31 at 13:42 -0800, John Hubbard wrote: > > On 1/31/26 11:00 AM, Matthew Brost wrote: > > > On Sat, Jan 31, 2026 at 01:57:21PM +0100, Thomas Hellström wrote: > > > > On Fri, 2026-01-30 at 19:01 -0800, John Hubbard wrote: > > > > > On 1/30/26 10:00 AM, Andrew Morton wrote: > > > > > > On Fri, 30 Jan 2026 15:45:29 +0100 Thomas Hellström > > > > > > wrote: > > > > > ... > > > > > > > > > I'm also not sure a folio refcount should block migration after > > > > the > > > > introduction of pinned (like in pin_user_pages) pages. Rather > > > > perhaps a > > > > folio pin-count should block migration and in that case > > > > do_swap_page() > > > > can definitely do a sleeping folio lock and the problem is gone. > > > > A problem for that specific point is that pincount and refcount both > > mean, "the page is pinned" (which in turn literally means "not > > allowed > > to migrate/move"). > > Yeah this is what I actually want to challenge since this is what > blocks us from doing a clean robust solution here. From brief reading > of the docs around the pin-count implementation, I understand it as "If > you want to access the struct page metadata, get a refcount, If you > want to access the actual memory of a page, take a pin-count" > > I guess that might still not be true for all old instances in the > kernel using get_user_pages() instead of pin_user_pages() for things > like DMA, but perhaps we can set that in stone and document it at least > for device-private pages for now which would be sufficient for the > do_swap_pages() refcount not to block migration. Having just spent a long time cleaning up a bunch of special rules/cases for ZONE_DEVICE page refcounting I'm rather against reintroducing them just for some ZONE_DEVICE pages. So whatever arguments are applied or introduced here would need to be made to work for all pages, not just some ZONE_DEVICE pages. > > > > (In fact, pincount is implemented in terms of refcount, in most > > configurations still.) > > Yes but that's only a space optimization never intended to conflict, > right? Meaning a pin-count will imply a refcount but a refcount will > never imply a pin-count? > > Thanks, > Thomas >