Re: [PATCH v4 0/2] mm: improve folio refcount scalability

[Linus Torvalds]

On Sat, 20 Jun 2026 at 11:19, <ilya.gladyshev@xxxxxxxxx> wrote:
>
> T2: optimistic get() [0 -> 1]
> T2: put page back [1 -> 0]
> T2: calls dtor for type X, returns into the allocator

Which optimistic getter does this?

I didn't go back and look at the series, but isn't the rule that the code does:

 - optimistic get

 - then check that the folio is still valid (*not* using the page
count, but by re-looking it up elsewhere, typically the address space
mapping)

 - put the page if it wasn't valid

 - if it goes to zero, there's no destructor inherent in that

 - everybody who sees it go to zero - optimistic or not - does the
"zero to frozen" cmpxchg

 - only *one* of those will succeed, and *THAT* triggers the destructor

IOW, the transition to zero is not special per se and has no
destructor. All it triggers is the "now we try to mark it frozen"
phase.

At least that was my mental picture.

Was I wrong? Am I just confused? Wouldn't be the first time.

             Linus