Re: [PATCH 1/3] mm/mincore: make mincore() more conservative

[Dominique Martinet]

Michal Hocko wrote on Thu, Jan 31, 2019:
> > Change the semantics of mincore() so that it only reveals pagecache information
> > for non-anonymous mappings that belog to files that the calling process could
> > (if it tried to) successfully open for writing.
> 
> I agree that this is a better way than the original 574823bfab82
> ("Change mincore() to count "mapped" pages rather than "cached" pages").
> One thing is still not clear to me though. Is the new owner/writeable
> check OK for the Netflix-like usecases? I mean does happycache have
> appropriate access to the cache data? I have tried to re-read the
> original thread but couldn't find any confirmation.

It's enough for my use cases and Josh didn't seem to oppose, but since
he's not in Cc I don't think he would answer -- added him now :)

FWIW happycache writes in the current directory by default so I assume
in the way they use it it would usually have access one way or another.

> If this still doesn't help happycache kind of workloads then we should
> add a capability check IMO but this looks like a decent foundation to
> me.

the inode_owner_or_capable/inode_permission helpers already do allow
quite a few capabilities there


-- 
Dominique