Re: [PATCH 04/11] mm: compaction: export some of the functions

[Michal Nazarewicz]

On Mon, 12 Dec 2011 15:29:07 +0100, Mel Gorman <mel@xxxxxxxxx> wrote:

> On Fri, Nov 18, 2011 at 05:43:11PM +0100, Marek Szyprowski wrote:
> > From: Michal Nazarewicz <mina86@xxxxxxxxxx>
> >
> > This commit exports some of the functions from compaction.c file
> > outside of it adding their declaration into internal.h header
> > file so that other mm related code can use them.
> >
> > This forced compaction.c to always be compiled (as opposed to being
> > compiled only if CONFIG_COMPACTION is defined) but as to avoid
> > introducing code that user did not ask for, part of the compaction.c
> > is now wrapped in on #ifdef.
> >
> > Signed-off-by: Michal Nazarewicz <mina86@xxxxxxxxxx>
> > Signed-off-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
> > ---
> >  mm/Makefile     |    3 +-
> >  mm/compaction.c |  112 +++++++++++++++++++++++--------------------------------
> >  mm/internal.h   |   35 +++++++++++++++++
> >  3 files changed, 83 insertions(+), 67 deletions(-)
> >
> > diff --git a/mm/Makefile b/mm/Makefile
> > index 50ec00e..24ed801 100644
> > --- a/mm/Makefile
> > +++ b/mm/Makefile
> > @@ -13,7 +13,7 @@ obj-y			:= filemap.o mempool.o oom_kill.o fadvise.o \
> >  			   readahead.o swap.o truncate.o vmscan.o shmem.o \
> >  			   prio_tree.o util.o mmzone.o vmstat.o backing-dev.o \
> >  			   page_isolation.o mm_init.o mmu_context.o percpu.o \
> > -			   $(mmu-y)
> > +			   $(mmu-y) compaction.o
>
> That should be
>
> compaction.o $(mmu-y)
>
> for consistency.
>
> Overall, this patch implies that CMA is always compiled in.

Not really.  But yes, it produces some bloat when neither CMA nor
compaction are compiled.  I assume that linker will be able to deal
with that (since the functions are not EXPORT_SYMBOL'ed).

Note also that the was majority of compaction.c is #ifdef'd though
so only a handful of functions are compiled.

> Why not just make CMA depend on COMPACTION to keep things simplier?

I could imagine that someone would want to have CMA but not compaction,
hence I decided to give that choice.

> For example, if you enable CMA and do not enable COMPACTION, you
> lose things like the vmstat counters that can aid debugging. In
> fact, as parts of compaction.c are using defines like COMPACTBLOCKS,
> I'm not even sure compaction.c can compile without CONFIG_COMPACTION
> because of the vmstat stuff.

--
Best regards,                                         _     _
.o. | Liege of Serenely Enlightened Majesty of      o' \,=./ `o
..o | Computer Science,  MichaÅ âmina86â Nazarewicz    (o o)
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