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 c7A4fNQc 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 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 2/2/26 1:13 AM, 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. > It's an interesting direction to go... > >> >> (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? > Unfortunately, they are more tightly linked than that today, at least until someday when specialized folios are everywhere (at which point pincount gets its own field). Until then, it's not just a "space optimization", it's "overload refcount to also do pincounting". And "let core mm continue to treat refcounts as meaning that the page is pinned". thanks, -- John Hubbard