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

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Message-Id: <D3QWEFR2E2BZ.187FVXI3QQU9U@kernel.org>
Date: Tue, 27 Aug 2024 21:16:31 +0300
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Haitao Huang" <haitao.huang@...ux.intel.com>,
 <dave.hansen@...ux.intel.com>, <kai.huang@...el.com>, <tj@...nel.org>,
 <mkoutny@...e.com>, <chenridong@...wei.com>,
 <linux-kernel@...r.kernel.org>, <linux-sgx@...r.kernel.org>,
 <x86@...nel.org>, <cgroups@...r.kernel.org>, <tglx@...utronix.de>,
 <mingo@...hat.com>, <bp@...en8.de>, <hpa@...or.com>,
 <sohil.mehta@...el.com>, <tim.c.chen@...ux.intel.com>
Cc: <zhiquan1.li@...el.com>, <kristen@...ux.intel.com>, <seanjc@...gle.com>,
 <zhanb@...rosoft.com>, <anakrish@...rosoft.com>,
 <mikko.ylinen@...ux.intel.com>, <yangjie@...rosoft.com>,
 <chrisyan@...rosoft.com>
Subject: Re: [PATCH v16 12/16] x86/sgx: Revise global reclamation for EPC
 cgroups

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@...ux.intel.com>

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

BR, Jarkko