On 4/24/26 08:04, Peter Zijlstra wrote: > So I don't like this at all.... The comment says there is a preceding > TLB flush, but there is nothing that guarantees there is. One would have > to go audit all users and ensure this is always true. > > This thing is incredibly fragile.
Yeah, this seems like an attempt to apply a code solution to a data structure problem. I think I talked about this in earlier iterations. But, ideally, what happens here is that the things doing the table freeing or collapsing or whatever would note in a data structure what they did. Then the actual flushing code can look at the data structure and figure out what kind of flush it needs. Things like "do I need to flush on lazy CPUs?" Or, "have I done an IPI since the last page table free?" But, if I remember from earlier in this thread, some of the callers of this stuff didn't have a nice data structure (like an mmu_gather) passed in to the places where it would be needed to exfiltrate the information. I think Lance gave up on that because it looked too invasive to him. But, I think this boils down to the code being too fragile as-is to support what Lance is trying to do. It actually needs some refactoring love before it can support the desired optimization. I'm not sure there's an easy way out here.
