Re: [RFC] memory defragmentation to satisfy high order allocations

[Marcelo Tosatti <marcelo.tosatti@cyclades.com>]

On Mon, Oct 04, 2004 at 01:09:10PM +0900, IWAMOTO Toshihiro wrote:
> At Sat, 2 Oct 2004 15:33:49 -0300,
> Marcelo Tosatti wrote:
> > 
> > On Sat, Oct 02, 2004 at 06:30:15PM +0900, Hirokazu Takahashi wrote:
> > 3) At migrate_page_common you assume additional page references 
> > (page_migratable returning -EAGAIN) means the code should try to writeout 
> > the page.
> > 
> > Is that assumption always valid?
> > 
> > In theory there is no need to writeout pages when migrating them to 
> > other zones - they will be copied and the dirty information retained (either
> > in the PageDirty bit or radix tree tag). 
> 
> It's true only when page->private is NULL.  Otherwise writeback is
> necessary to free buffer_head.

You can move the buffer_head's also cant you? Adjusting bh->b_page etc.

Thats what migrate_page_buffer does, no?

Writting pages which contain buffer_head's on memory migration
is really, very bad. 

Imagine gigabytes of pages with buffer_head's. 

> > I just noticed you do that on further patches (migrate_page_buffer), but AFAICS 
> > the writeout remains. Why arent you using migrate_page_buffer yet?
> > 
> > I think the final aim should be to remove the need for "pageout()" 
> > completly.
> 
> Are you going to implement migrate_page_buffer for every file system?
> I don't think it's worthwhile.
> 
> > Questions: are there any documents on the memory hotplug userspace tools? 
> > Where can I find them?
> > 
> > Are Iwamoto's test programs available?
> 
> I've put them at the following URL, but I doubt they are useful for
> you; there are no documentation for them.
> 
> http://people.valinux.co.jp/~iwamoto/mh/tests/

I'll take a look thanks.