Re: [PATCH] 9p: avoid attaching writeback_fid on mmap with type PRIVATE

From: Dominique Martinet
Date: Tue Aug 20 2019 - 07:49:46 EST

Chengguang Xu wrote on Tue, Aug 20, 2019:
> Currently on mmap cache policy, we always attach writeback_fid
> whether mmap type is SHARED or PRIVATE. However, in the use case
> of kata-container which combines 9p(Guest OS) with overlayfs(Host OS),
> this behavior will trigger overlayfs' copy-up when excute command
> inside container.

hmm, I guess this just works for non-ovl cases because sync_inode()
realizes there is nothing to sync, but the fsync at the end still
triggers the copy-up ?

Well, I guess there really is no need to flush for private mappings,
so might as well go for this; sparing an extra useless clone walk cannot

I'll queue this up after tests, no promise on delay sorry :/