linux-kernel - Re: [patch 2/5] Reinstate ZERO_PAGE optimization in get_user

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Date:	Tue, 24 Jun 2008 01:05:04 +0800
From:	"Jeff Chua" <jeff.chua.linux@...il.com>
To:	"Linus Torvalds" <torvalds@...ux-foundation.org>
Cc:	"Hugh Dickins" <hugh@...itas.com>, "Greg KH" <gregkh@...e.de>,
	linux-kernel@...r.kernel.org, stable@...nel.org,
	"Justin Forbes" <jmforbes@...uxtx.org>,
	"Zwane Mwaikambo" <zwane@....linux.org.uk>,
	"Theodore Ts'o" <tytso@....edu>,
	"Randy Dunlap" <rdunlap@...otime.net>,
	"Dave Jones" <davej@...hat.com>,
	"Chuck Wolber" <chuckw@...ntumlinux.com>,
	"Chris Wedgwood" <reviews@...cw.f00f.org>,
	"Michael Krufky" <mkrufky@...uxtv.org>,
	"Chuck Ebbert" <cebbert@...hat.com>,
	"Domenico Andreoli" <cavokz@...il.com>, "Willy Tarreau" <w@....eu>,
	"Rodrigo Rubira Branco" <rbranco@...checkpoint.com>,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	"Oleg Nesterov" <oleg@...sign.ru>, "Nick Piggin" <npiggin@...e.de>,
	"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>,
	"Ingo Molnar" <mingo@...e.hu>, "Roland McGrath" <roland@...hat.com>
Subject: Re: [patch 2/5] Reinstate ZERO_PAGE optimization in get_user_pages() and fix XIP

On Tue, Jun 24, 2008 at 12:39 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:

> So here's a third patch to test. It removes the VM_SHARED thing just to
> get us closer to the original code (and because do_no_page() didn't do it
> historically, so let's not do it either), and it re-instates the insane
> VM_LOCKED test with a comment.
>
> Jeff, does this still work with vmware?


No, this breaks vmware. Does this trace help?

Jun 24 00:54:49.325: vmx| NOT_IMPLEMENTED
/build/mts/release/bora-93057/bora/vmx/main/vmmonPosix.c:774
Jun 24 00:54:49.325: vmx| Backtrace:
Jun 24 00:54:49.325: vmx| Backtrace[0] 0xbffc30c8 eip 0x8052f10
Jun 24 00:54:49.325: vmx| Backtrace[1] 0xbffc34f8 eip 0x80f2f7d
Jun 24 00:54:49.325: vmx| Backtrace[2] 0xbffc3548 eip 0x80e4b15
Jun 24 00:54:49.325: vmx| Backtrace[3] 0xbffc3638 eip 0x837b341
Jun 24 00:54:49.325: vmx| Backtrace[4] 0xbffc3688 eip 0x837cde4
Jun 24 00:54:49.325: vmx| Backtrace[5] 0xbffc36b8 eip 0x80fda89
Jun 24 00:54:49.325: vmx| Backtrace[6] 0xbffc36e8 eip 0x80f36f5
Jun 24 00:54:49.325: vmx| Backtrace[7] 0xbffc3728 eip 0x80f3bd4
Jun 24 00:54:49.325: vmx| Backtrace[8] 0xbffc3788 eip 0x80511be
Jun 24 00:54:49.325: vmx| Backtrace[9] 0xbffc3878 eip 0x8051561
Jun 24 00:54:49.325: vmx| Backtrace[10] 0xbffc38e8 eip 0xb7e374c0
Jun 24 00:54:49.325: vmx| Backtrace[11] 00000000 eip 0x804e7b1
Jun 24 00:54:49.325: vmx| Core dump limit is 0 kb.
Jun 24 00:54:49.326: vmx| Cannot remap region MonWired (addr=(nil),
size=0x13000, offset=0x19000)
Jun 24 00:54:49.326: vmx| Cannot remap region PShareMPN (addr=(nil),
size=0x1000, offset=0x18000)
Jun 24 00:54:49.326: vmx| Remapping region BusMemFrame1 as MAP_PRIVATE
(addr=0xb7f9c000, size=0x1000, offset=0x17000)
Jun 24 00:54:49.326: vmx| Remapping region BusMemFrame0 as MAP_PRIVATE
(addr=0xb7f9d000, size=0x1000, offset=0x16000)
Jun 24 00:54:49.326: vmx| Cannot remap region PhysRegion0 (addr=(nil),
size=0x1000, offset=0x15000)
Jun 24 00:54:49.326: vmx| Msg_Post: Error
Jun 24 00:54:49.326: vmx| [msg.log.error.unrecoverable] VMware
Workstation unrecoverable error: (vmx)
Jun 24 00:54:49.326: vmx| NOT_IMPLEMENTED
/build/mts/release/bora-93057/bora/vmx/main/vmmonPosix.c:774


Thanks,
Jeff.




>  mm/memory.c |   20 ++++++++++++++++++--
>  1 files changed, 18 insertions(+), 2 deletions(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index 9aefaae..a2ce28d 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -1045,6 +1045,23 @@ no_page_table:
>        return page;
>  }
>
> +/* Can we do the FOLL_ANON optimization? */
> +static inline int use_zero_page(struct vm_area_struct *vma)
> +{
> +       /*
> +        * We don't want to optimize FOLL_ANON for make_pages_present()
> +        * when it tries to page in a VM_LOCKED region.
> +        */
> +       if (vma->vm_flags & VM_LOCKED)
> +               return 0;
> +       /*
> +        * And if we have a fault or a nopfn routine, it's not an
> +        * anonymous region.
> +        */
> +       return !vma->vm_ops ||
> +               (!vma->vm_ops->fault && !vma->vm_ops->nopfn);
> +}
> +
>  int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
>                unsigned long start, int len, int write, int force,
>                struct page **pages, struct vm_area_struct **vmas)
> @@ -1119,8 +1136,7 @@ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
>                foll_flags = FOLL_TOUCH;
>                if (pages)
>                        foll_flags |= FOLL_GET;
> -               if (!write && !(vma->vm_flags & VM_LOCKED) &&
> -                   (!vma->vm_ops || !vma->vm_ops->fault))
> +               if (!write && use_zero_page(vma))
>                        foll_flags |= FOLL_ANON;
>
>                do {
>
--
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