Re: [PATCH 2/2] mm: adds NOSIGBUS extension for out-of-band shmem read

On Jun 3, 2021, at 12:14 PM, Linus Torvalds [off-list ref] wrote:

On Thu, Jun 3, 2021 at 12:07 PM Hugh Dickins [off-list ref] wrote:

quoted

But the point that we've arrived at, that I'm actually now fairly
happy with, is do *not* permit MAP_NOSIGBUS on MAP_SHARED mappings.

Yeah, if that's sufficient, then that original patch should just work as-is.

But there was some reason why people didn't like that patch
originally, and I think it was literally about how it only worked on
private mappings (the "we don't have a flag for it in the vm_flags"
part was just a small detail.

I guess that objection ended up changing over time.

I don’t understand the use case well enough to comment on whether MAP_PRIVATE is sufficient, but I’m with Hugh: if this feature is implemented for MAP_SHARED, it should be fully coherent.