linux-kernel - Re: [PATCH 24/25] x86/sgx: Free up EPC pages directly to support large page ranges

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Date:   Sun, 5 Dec 2021 01:47:00 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Reinette Chatre <reinette.chatre@...el.com>
Cc:     dave.hansen@...ux.intel.com, tglx@...utronix.de, bp@...en8.de,
        luto@...nel.org, mingo@...hat.com, linux-sgx@...r.kernel.org,
        x86@...nel.org, seanjc@...gle.com, kai.huang@...el.com,
        cathy.zhang@...el.com, cedric.xing@...el.com,
        haitao.huang@...el.com, mark.shanahan@...el.com, hpa@...or.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 24/25] x86/sgx: Free up EPC pages directly to support
 large page ranges

On Wed, Dec 01, 2021 at 11:23:22AM -0800, Reinette Chatre wrote:
> The page reclaimer ensures availability of EPC pages across all
> enclaves. In support of this it runs independently from the individual
> enclaves in order to take locks from the different enclaves as it writes
> pages to swap.
> 
> When needing to load a page from swap an EPC page needs to be available for
> its contents to be loaded into. Loading an existing enclave page from swap
> does not reclaim EPC pages directly if none are available, instead the
> reclaimer is woken when the available EPC pages are found to be below a
> watermark.
> 
> When iterating over a large number of pages in an oversubscribed
> environment there is a race between the reclaimer woken up and EPC pages
> reclaimed fast enough for the page operations to proceed.
> 
> Instead of tuning the race between the page operations and the reclaimer
> the page operations instead makes sure that there are EPC pages available.
> 
> Signed-off-by: Reinette Chatre <reinette.chatre@...el.com>

Why this needs to be part of this patch set?

/Jarkko