linux-kernel - Re: [PATCH] mm: Add new vma flag VM_LOCAL

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Message-ID: <20180522165641.GN12217@hirez.programming.kicks-ass.net>
Date:   Tue, 22 May 2018 18:56:41 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Christopher Lameter <cl@...ux.com>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Boaz Harrosh <boazh@...app.com>,
        Jeff Moyer <jmoyer@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Rik van Riel <riel@...hat.com>, Jan Kara <jack@...e.cz>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        Amit Golander <Amit.Golander@...app.com>
Subject: Re: [PATCH] mm: Add new vma flag VM_LOCAL_CPU

On Tue, May 22, 2018 at 04:46:05PM +0000, Christopher Lameter wrote:
> On Tue, 22 May 2018, Dave Hansen wrote:
> 
> > On 05/22/2018 09:05 AM, Boaz Harrosh wrote:
> > > How can we implement "Private memory"?
> >
> > Per-cpu page tables would do it.
> 
> We already have that for percpu subsystem. See alloc_percpu()

x86 doesn't have per-cpu page tables. And the last time I looked, percpu
also didn't, it played games with staggered ranges in the vmalloc space
and used the [FG]S segment offset to make it work.

Doing proper per-cpu pagetables on x86 is possible, but quite involved
and expensive.