Re: [PATCH v16 12/16] x86/sgx: Revise global reclamation for EPC cgroups

["Jarkko Sakkinen" <jarkko@kernel.org>]

On Wed Aug 21, 2024 at 4:54 AM EEST, Haitao Huang wrote:
> With EPC cgroups, the global reclamation function,
> sgx_reclaim_pages_global(), can no longer apply to the global LRU as
> pages are now in per-cgroup LRUs.
>
> Create a wrapper, sgx_cgroup_reclaim_global() to invoke
> sgx_cgroup_reclaim_pages() passing in the root cgroup. Call this wrapper
> from sgx_reclaim_pages_global() when cgroup is enabled. The wrapper will
> scan and attempt to reclaim SGX_NR_TO_SCAN pages just like the current
> global reclaim.
>
> Note this simple implementation doesn't _exactly_ mimic the current
> global EPC reclaim (which always tries to do the actual reclaim in batch
> of SGX_NR_TO_SCAN pages): in rare cases when LRUs have less than
> SGX_NR_TO_SCAN reclaimable pages, the actual reclaim of EPC pages will
> be split into smaller batches _across_ multiple LRUs with each being
> smaller than SGX_NR_TO_SCAN pages.
>
> A more precise way to mimic the current global EPC reclaim would be to
> have a new function to only "scan" (or "isolate") SGX_NR_TO_SCAN pages
> _across_ the given EPC cgroup _AND_ its descendants, and then do the
> actual reclaim in one batch.  But this is unnecessarily complicated at
> this stage to address such rare cases.
>
> Signed-off-by: Haitao Huang <haitao.huang@linux.intel.com>

Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>

BR, Jarkko