Re: memory hotplug: hot-add to ZONE_MOVABLE vs. min_free_kbytes

[Gerald Schaefer <gerald.schaefer@de.ibm.com>]

On Fri, 2008-08-01 at 20:16 +0900, Yasunori Goto wrote:
> > My assumption is now, that the reserved 3 MB in ZONE_MOVABLE won't be
> > usable by the kernel anymore, e.g. for PF_MEMALLOC, because it is in
> > ZONE_MOVABLE now.
> 
> I don't make sense here. I suppose there is no relationship between
> ZONE_MOVABLE, PF_MEMALLOC and MIGRATE_RESERVE pages.
> Could you tell me more?

Ok, I thought that PF_MEMALLOC allocations work on the MIGRATE_RESERVE
pageblocks, and that only kernel allocations can use PF_MEMALLOC. I also
thought that kernel allocations cannot use ZONE_MOVABLE, e.g. for page
cache memory, because such pages would not be migratable. So I assumed
that MIGRATE_RESERVE pageblocks in ZONE_MOVABLE would not be available
for PF_MEMALLOC allocations.

With this assumption, which can be totally wrong, the redistribution
of MIGRATE_RESERVE pageblocks in setup_per_zone_pages_min() looks like
it will take away reserved pageblocks that should be available to the
kernel in emergency situations.

Maybe I should have explained this assumption earlier, because my whole
min_free_kbytes issue depends on it. If I'm wrong, I apologize for
confusing you all with this "issue", and I will go back to the original
problem with removing the lowest memory chunk in ZONE_MOVABLE...

Thanks,
Gerald


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