> On Jan 15, 2019, at 9:00 PM, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > >> 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.. > > Something like CAP_DAC_READ_SEARCH might not be crazy.
