Messages in this thread | | | From | Linus Torvalds <> | Date | Wed, 16 Jan 2019 17:00:25 +1200 | Subject | Re: [PATCH] mm/mincore: allow for making sys_mincore() privileged |
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On Wed, Jan 16, 2019 at 12:42 PM Josh Snyder <joshs@netflix.com> 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
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