On Wed, Jan 16, 2019 at 12:42 PM Josh Snyder <joshs@xxxxxxxxxxx> wrote:
>
> For Netflix, losing accurate information from the mincore syscall would
> lengthen database cluster maintenance operations from days to months. We
> rely on cross-process mincore to migrate the contents of a page cache from
> machine to machine, and across reboots.
Ok, this is the kind of feedback we need, and means I guess we can't
just use the mapping existence for mincore.
The two other ways that we considered were:
(a) owner of the file gets to know cache information for that file.
(b) having the fd opened *writably* gets you cache residency information.
Sadly, taking a look at happycache, you open the file read-only, so
(b) doesn't work.
Judging just from the source code, I can't tell how the user ownership
works. Any input on that?
And if you're not the owner of the file, do you have another
suggestion for that "Yes, I have the right to see what's in-core for
this file". Because the problem is literally that if it's some random
read-only system file, the kernel shouldn't leak access patterns to
it..
Linus
