linux-kernel - Re: [PATCH v28 16/22] x86/sgx: Add a page reclaimer

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Message-ID: <20200315002732.GA208715@linux.intel.com>
Date:   Sun, 15 Mar 2020 02:27:32 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-sgx@...r.kernel.org, akpm@...ux-foundation.org,
        dave.hansen@...el.com, nhorman@...hat.com, npmccallum@...hat.com,
        haitao.huang@...el.com, andriy.shevchenko@...ux.intel.com,
        tglx@...utronix.de, kai.svahn@...el.com, bp@...en8.de,
        josh@...htriplett.org, luto@...nel.org, kai.huang@...el.com,
        rientjes@...gle.com, cedric.xing@...el.com, puiterwijk@...hat.com,
        linux-mm@...ck.org, Ismo Puustinen <ismo.puustinen@...el.com>,
        Mark Shanahan <mark.shanahan@...el.com>,
        Mikko Ylinen <mikko.ylinen@...el.com>,
        Derek Bombien <derek.bombien@...el.com>
Subject: Re: [PATCH v28 16/22] x86/sgx: Add a page reclaimer

On Thu, Mar 12, 2020 at 11:38:24AM -0700, Sean Christopherson wrote:
> On Fri, Mar 06, 2020 at 08:47:02PM +0200, Jarkko Sakkinen wrote:
> > On Thu, Mar 05, 2020 at 11:03:54AM -0800, Sean Christopherson wrote:
> > > We've also discussed taking a file descriptor to hold the backing, but
> > > unless I'm misreading the pagecache code, that doesn't solve the incorrect
> > > accounting problem because the current task, i.e. evicting task, would be
> > > charged.  In other words, whether the backing is kernel or user controlled
> > > is purely an ABI question.
> > 
> > Even if the file is owned by a different process the account happens
> > to "current"?
> 
> Yes.  Which makes sense as files do not have a 1:1 association with tasks.

Yeah, that makes sense. Looking at mm/memory.c.

Looking at finish_fault/alloc_set_pte/inc_mm_counter_fast code path that
is also what happens.

/Jarkko