On Wed, 27 Sep 2023 06:35:57 -0500, Huang, Kai <kai.huang@xxxxxxxxx> wrote:
On Fri, 2023-09-22 at 20:06 -0700, Haitao Huang wrote:
From: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
In a later patch, when a cgroup has exceeded the max capacity for EPC
pages, it may need to identify and OOM kill a less active enclave to
make room for other enclaves within the same group. Such a victim
enclave would have no active pages other than the unreclaimable Version
Array (VA) and SECS pages.
What does "no active pages" mean?
EPC pages in use.
A "less active enclave" doesn't necessarily mean it has "no active
pages"?
I'll rephrase the above sentences
Therefore, the cgroup needs examine its
^
needs to
unreclaimable page list, and finding an enclave given a SECS page or a
^
find
VA page. This will require a backpointer from a page to an enclave,
which is not available for VA pages.
Because struct sgx_epc_page instances of VA pages are not owned by an
sgx_encl_page instance, mark their owner as sgx_encl: pass the struct
sgx_encl of the enclave allocating the VA page to sgx_alloc_epc_page(),
which will store this value in the owner field of the struct
sgx_epc_page.
IMHO this paragraph is hard to understand and can be more concise:
One VA page can be shared by multiple enclave pages thus cannot be
associated
with any 'struct sgx_encl_page' instance. Set the owner of VA page to
the
enclave instead.
Agreed
In a later patch, VA pages will be placed in an
unreclaimable queue that can be examined by the cgroup to select the OOM
killed enclave.
The code to "place the VA page to unreclaimable queue" has been done in
earlier
patch ("x86/sgx: Introduce EPC page states"). Just the unreclaimable
list isn't
introduced yet. I think you should just introduce it first then you can
get rid
of those "in a later patch" staff.
I hope I was able to clarify to you in other threads that VA pages are not
placed in any queue/list until [PATCH v5 11/18] x86/sgx: store
unreclaimable pages in LRU lists.
This patch is the first one to implement tracking for unreclaimable pages.
I'll add that as a transition hint.
And nit: please use "unreclaimable list" consistently (not queue).
Yes will do
Btw, probably a dumb question:
Theoretically if you only need to find a victim enclave you don't need
to put VA
pages to the unreclaimable list, because those VA pages will be freed
anyway
when enclave is killed. So keeping VA pages in the list is for
accounting all
the pages that the cgroup is having?
Yes basically tracking them in cgroups as they are allocated.
VAs and SECS may also come and go as swapping/unswapping happens. But if a
cgroup is OOM, and all reclaimables are gone (swapped out), it'd have to
reclaim VAs/SECs in the same cgroup starting from the front of the LRU
list. To reclaim a VA/SECS, it identifies the enclave from the owner of
the VA/SECS page and kills it, as killing enclave is the only way to
reclaim VA/SECS pages.
