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

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Message-ID: <YEilecZyT93xdtc1@kernel.org>
Date:   Wed, 10 Mar 2021 12:54:49 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     linux-sgx@...r.kernel.org,
        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 Wed, Mar 03, 2021 at 03:48:46PM -0800, Dave Hansen wrote:
> 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?

These are per-section structures, not per-node structures. Probably most
times, if not all times, they are equal, but conceptually I'm not
destroying per-node structures :-) I'm introducing them in 5/5.

/Jarkko