[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20160128213302.GB4163@cmpxchg.org>
Date: Thu, 28 Jan 2016 16:33:02 -0500
From: Johannes Weiner <hannes@...xchg.org>
To: Andy Lutomirski <luto@...capital.net>
Cc: Andy Lutomirski <luto@...nel.org>, Hugh Dickins <hughd@...gle.com>,
Andrew Morton <akpm@...ux-foundation.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: do not let vdso pages into LRU rotation
On Wed, Jan 27, 2016 at 12:32:16PM -0800, Andy Lutomirski wrote:
> On Wed, Jan 27, 2016 at 11:39 AM, Johannes Weiner <hannes@...xchg.org> wrote:
> > Could the VDSO be a VM_MIXEDMAP to keep the initial unmanaged pages
> > out of the VM while allowing COW into regular anonymous pages?
>
> Probably. What are its limitations? We want ptrace to work on it,
> and mprotect needs to work and allow COW. access_process_vm should
> probably work, too.
Thanks, that's good to know.
However, after looking at this a little longer, it appears this would
need work in do_wp_page() to support non-page COW copying, then adding
vm_ops->access and complicating ->fault in all VDSO implementations.
And it looks like - at least theoretically - drivers can inject non-VM
pages into the page tables as well (comment above insert_page())
Given that this behavior has been around for a long time (the comment
at the bottom of vm_normal_page is ancient), I'll probably go with a
more conservative approach; add a comment to mark_page_accessed() and
filter out non-VM pages in the function I'm going to call from it.
Thanks!
Powered by blists - more mailing lists