Re: [PATCH 04/11] Allow CONFIG_MIGRATION to be set withoutCONFIG_NUMA or memory hot-remove

[Mel Gorman]

On Wed, Mar 17, 2010 at 11:28:26AM +0900, KOSAKI Motohiro wrote:
> > CONFIG_MIGRATION currently depends on CONFIG_NUMA or on the architecture
> > being able to hot-remove memory. The main users of page migration such as
> > sys_move_pages(), sys_migrate_pages() and cpuset process migration are
> > only beneficial on NUMA so it makes sense.
> > 
> > As memory compaction will operate within a zone and is useful on both NUMA
> > and non-NUMA systems, this patch allows CONFIG_MIGRATION to be set if the
> > user selects CONFIG_COMPACTION as an option.
> > 
> > Signed-off-by: Mel Gorman <mel@xxxxxxxxx>
> > Reviewed-by: Christoph Lameter <cl@xxxxxxxxxxxxxxxxxxxx>
> > Reviewed-by: Rik van Riel <riel@xxxxxxxxxx>
> > Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> > ---
> >  mm/Kconfig |   20 ++++++++++++++++----
> >  1 files changed, 16 insertions(+), 4 deletions(-)
> > 
> > diff --git a/mm/Kconfig b/mm/Kconfig
> > index 9c61158..04e241b 100644
> > --- a/mm/Kconfig
> > +++ b/mm/Kconfig
> > @@ -172,17 +172,29 @@ config SPLIT_PTLOCK_CPUS
> >  	default "4"
> >  
> >  #
> > +# support for memory compaction
> > +config COMPACTION
> > +	bool "Allow for memory compaction"
> > +	def_bool y
> > +	select MIGRATION
> > +	depends on EXPERIMENTAL && HUGETLBFS && MMU
> > +	help
> > +	  Allows the compaction of memory for the allocation of huge pages.
> > +
> 
> If select MIGRATION works, we can remove "depends on NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE"
> line from config MIGRATION.
> 

I'm not quite getting why this would be an advantage. COMPACTION
requires MIGRATION but conceivable both NUMA and HOTREMOVE can work
without it.

> 
> 
> > +#
> >  # support for page migration
> >  #
> >  config MIGRATION
> >  	bool "Page migration"
> >  	def_bool y
> > -	depends on NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE
> > +	depends on NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE || COMPACTION
> >  	help
> >  	  Allows the migration of the physical location of pages of processes
> > -	  while the virtual addresses are not changed. This is useful for
> > -	  example on NUMA systems to put pages nearer to the processors accessing
> > -	  the page.
> > +	  while the virtual addresses are not changed. This is useful in
> > +	  two situations. The first is on NUMA systems to put pages nearer
> > +	  to the processors accessing. The second is when allocating huge
> > +	  pages as migration can relocate pages to satisfy a huge page
> > +	  allocation instead of reclaiming.
> >  
> >  config PHYS_ADDR_T_64BIT
> >  	def_bool 64BIT || ARCH_PHYS_ADDR_T_64BIT
> > -- 
> > 1.6.5
> > 
> 
> 
> 

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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