linux-kernel - Re: [PATCH v3 4/5] x86/sgx: Replace section->page

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Date:   Wed, 3 Mar 2021 15:48:46 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Jarkko Sakkinen <jarkko@...nel.org>, linux-sgx@...r.kernel.org
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 4/5] x86/sgx: Replace section->page_list with a global
 free page list

On 3/3/21 7:03 AM, Jarkko Sakkinen wrote:
> Background
> ==========
> 
> EPC section is covered by one or more SRAT entries that are associated with
> one and only one PXM (NUMA node). The current implementation overheats a

Overheats?

> single NUMA node, because sgx_alloc_epc_page() always starts looking for
> pages from the same EPC section everytime.

"every time"

> Only within a section it does pick pages in FIFO fashion, i.e. the oldest
> freed in that section is the EPC page given back to the caller.  That does
> not do any good, as the pages in the same node are performance-wise equal.

I'm not sure why all of this is relevant and it doesn't really tell me
anything about this patch's place in the *series*.

Why are we destroying all of the per-node structures just before adding
NUMA support?

> Replace local lists with a single global free page list, from which pages
> are borrowed in FIFO fashion.