On 1/18/12 6:42 PM, KAMEZAWA Hiroyuki wrote:
Hmm, then,
1. a new task jumped into this cgroup can see any uncleared data...
2. if a memcg pointer is reused, the information will be leaked.
You're suggesting mm_match_cgroup() is good enough for accounting
purposes, but not usable for cases where its important to get the
equality right?
3. If VM_UNINITALIZED is set, the process can see any data which
was freed by other process which doesn't know VM_UNINITALIZED at all.
4. The process will be able to see file cache data which the it has no
access right if it's accessed by memcg once.
3& 4 seems too danger.
Yes - these are the risks that I'm hoping we can document, so the
cgroups admin can avoid opting-in if not everything running in the
cgroup is trusted.
Isn't it better to have this as per-task rather than per-memcg ?
And just allow to reuse pages the page has freed ?
I'm worrying that the additional complexity of maintaining a per-task
page list would be a problem. It might slow down workloads that
alloc/free a lot because of the added code. It'll probably touch the
kswapd as well (for reclaiming pages from the per-task free lists under
low mem conditions).
Did you have some implementation ideas which would not have the problems
above?
-Arun
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