linux-kernel - Re: [patch 4/6] mm: merge populate and nopage into fault (fixes nonlinear)

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Thu, 8 Mar 2007 13:39:29 +0100
From:	Blaisorblade <blaisorblade@...oo.it>
To:	Bill Irwin <bill.irwin@...cle.com>
Cc:	Nick Piggin <npiggin@...e.de>, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Memory Management <linux-mm@...ck.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [patch 4/6] mm: merge populate and nopage into fault (fixes nonlinear)

On Wednesday 07 March 2007 10:44, Bill Irwin wrote:
> On Wed, Mar 07, 2007 at 10:28:21AM +0100, Nick Piggin wrote:
> > Depending on whether anyone wants it, and what features they want, we
> > could emulate the old syscall, and make a new restricted one which is
> > much less intrusive.
> > For example, if we can operate only on MAP_ANONYMOUS memory and specify
> > that nonlinear mappings effectively mlock the pages, then we can get
> > rid of all the objrmap and unmap_mapping_range handling, forget about
> > the writeout and msync problems...
>
> Anonymous-only would make it a doorstop for Oracle, since its entire
> motive for using it is to window into objects larger than user virtual
> address spaces (this likely also applies to UML, though they should
> really chime in to confirm).

We need it for shared file mappings (for tmpfs only).

Our scenario is:
RAM is implemented through a shared mapped file, kept on tmpfs (except by dumb 
users); various processes share an fd for this file (it's opened and 
immediately deleted).

We maintain page tables in x86 style, and TLB flush is implemented through 
mmap()/munmap()/mprotect().

Having a VMA per each 4K is not the intended VMA usage: for instance, the 
default /proc/sys/vm/max_map_count (64K) is saturated by a UML process with 
64K * 4K = 256M of resident memory.

> Restrictions to tmpfs and/or ramfs would 
> likely be liveable, though I suspect some things might want to do it to
> shm segments (I'll ask about that one).

> There's definitely no need for a 
> persistent backing store for the object to be remapped in Oracle's case,
> in any event. It's largely the in-core destination and source of IO, not
> something saved on-disk itself.
>
>
> -- wli

-- 
Inform me of my mistakes, so I can add them to my list!
Paolo Giarrusso, aka Blaisorblade
http://www.user-mode-linux.org/~blaisorblade
Chiacchiera con i tuoi amici in tempo reale! 
 http://it.yahoo.com/mail_it/foot/*http://it.messenger.yahoo.com 
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/