Fw: [Lhms-devel] Making hotremovable attribute with memory section[0/4]

Fw: [Lhms-devel] Making hotremovable attribute with memory section[0/4]

[Yasunori Goto]

Hello.

I made new patches for Memory hotplug. 
Dave Hansen-san recommeded me I should forward these to LKML
or linux-mm.
So, I'll forword these.

Please comment.

Thanks.


Forwarded by Yasunori Goto <ygoto@us.fujitsu.com>
----------------------- Original Message -----------------------
 From:    Yasunori Goto <ygoto@us.fujitsu.com>
 To:      lhms-devel@lists.sourceforge.net
 Date:    Mon, 16 Aug 2004 14:35:29 -0700
 Subject: [Lhms-devel] Making hotremovable attribute with memory section[0/4]
----

Hello.

Previous hot-removable attribute in my patches was only for node.
I made new patches to create hot-removable attribute
for memory section. 

This patches are for patch-2.6.8-rc4-mm1-mhp3.
(This is in http://sprucegoose.sr71.net/patches/)

Please comment.

Thanks.

-- 
Yasunori Goto <ygoto at us.fujitsu.com>




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--------------------- Original Message Ends --------------------

-- 
Yasunori Goto <ygoto at us.fujitsu.com>


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Re: Fw: [Lhms-devel] Making hotremovable attribute with memory section[0/4]

[Dave Hansen]

On Mon, 2004-08-16 at 15:56, Yasunori Goto wrote:
> I made new patches for Memory hotplug. 
> Dave Hansen-san recommeded me I should forward these to LKML
> or linux-mm.
> So, I'll forword these.

I think I suggested that you forward _one_ ;)

In any case, the question of the day is, does anyone have any
suggestions on how to create 2 separate pools for pages: one
representing hot-removable pages, and the other pages that may not be
removed?

Yasunori's patch takes the approach of creating a new free_area struct
inside each zone.  Another approach might be to actually create new
'struct zones' for the new areas.  The new zones one seems cleaner to
me, but the implementation might end up rippling in to a lot of
different areas of code.  

-- Dave

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Re: Fw: [Lhms-devel] Making hotremovable attribute with memory section[0/4]

[Alan Cox]

On Maw, 2004-08-17 at 00:35, Dave Hansen wrote:
> In any case, the question of the day is, does anyone have any
> suggestions on how to create 2 separate pools for pages: one
> representing hot-removable pages, and the other pages that may not be
> removed?

How do you define the split. There are lots of circumstances where user
pages can be pinned for a long (near indefinite) period of time and used
for DMA.

Consider
- Video capture
- AGP Gart
- AGP based framebuffer (intel i8/9xx)
- O_DIRECT I/O

There are also things like cluster interconnects, sendfile and the like
involved here.

Alan

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Re: [Lhms-devel] Making hotremovable attribute with memory section[0/4]

[Yasunori Goto]

Hello.

> On Maw, 2004-08-17 at 00:35, Dave Hansen wrote:
> > In any case, the question of the day is, does anyone have any
> > suggestions on how to create 2 separate pools for pages: one
> > representing hot-removable pages, and the other pages that may not be
> > removed?
> 
> How do you define the split. There are lots of circumstances where user
> pages can be pinned for a long (near indefinite) period of time and used
> for DMA.

Basically, kernel have to wait of completion of I/O.

> Consider
> - Video capture
> - AGP Gart
> - AGP based framebuffer (intel i8/9xx)

I didn't consider deeply about this, because usually
enterprise server doesn't need Video capture feature or AGP.
It is usually controlled from other machine.

If it is really necessary, kernel might have to wait 
I/O completion or driver modification is necessary.


> - O_DIRECT I/O

I can use page remmaping method by Iwamoto-san.
(See: http://people.valinux.co.jp/~iwamoto/mh.html#remap)
I guess that many case can be saved by this.

> There are also things like cluster interconnects, sendfile and the like
> involved here.

In sendfile case, kernel will wait too. Sooner or later, it will be
timeout.

Thank you for your comment.
Bye.

-- 
Yasunori Goto <ygoto at us.fujitsu.com>


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Re: Fw: [Lhms-devel] Making hotremovable attribute with memory section[0/4]

[Dave Hansen]

On Mon, 2004-08-16 at 17:27, Alan Cox wrote:
> On Maw, 2004-08-17 at 00:35, Dave Hansen wrote:
> > In any case, the question of the day is, does anyone have any
> > suggestions on how to create 2 separate pools for pages: one
> > representing hot-removable pages, and the other pages that may not be
> > removed?
> 
> How do you define the split.

We would hope not to have to define the split explicitly.  Since we're
hotplugging memory and resizing zones anyway, it shouldn't be a real
functional problem to balance memory between the 2 states, no matter how
it is implemented.  

> There are lots of circumstances where user
> pages can be pinned for a long (near indefinite) period of time and used
> for DMA.

For simple cases, anything tricky like DMA will simply be in an
unremovable area.  However, some platforms like ppc64 logical
partitions, require firmware notification of DMA areas.  The ppc64
firmware provides consistent remapping functionality for these DMA areas
if they ever need to be hot-swapped. 

> Consider
> - Video capture
> - AGP Gart
> - AGP based framebuffer (intel i8/9xx)
> - O_DIRECT I/O
> 
> There are also things like cluster interconnects, sendfile and the like
> involved here.

When we get to trying to forcefully migrate the kinds of memory that you
reference above, we'll likely need firmware support like ppc64 has.  The
other option is to have some driver callbacks to tell them to reallocate
their buffers into new areas, if that's even possible.  But, even that's
not something I see ever happening to the entire tree, more likely a
small subset of the drivers that really need it.  

-- Dave

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Re: [Lhms-devel] Making hotremovable attribute with memory section[0/4]

[Dave Jones]

On Mon, Aug 16, 2004 at 10:15:51PM -0700, Yasunori Goto wrote:
 > > Consider
 > > - Video capture
 > > - AGP Gart
 > > - AGP based framebuffer (intel i8/9xx)
 > 
 > I didn't consider deeply about this, because usually
 > enterprise server doesn't need Video capture feature or AGP.

AMD64's IOMMU is implemented using the AGP GART.
This feature is certainly used in server environments.

		Dave

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