Messages in this thread | | | Date | Thu, 31 Jul 2008 14:16:10 +0900 | From | Yasunori Goto <> | Subject | Re: memory hotplug: hot-remove fails on lowest chunk in ZONE_MOVABLE |
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> On Wed, 2008-07-30 at 12:16 +0900, Yasunori Goto wrote: > > Well, I didn't mean changing pages_min value. There may be side effect as > > you are saying. > > I meant if some pages were MIGRATE_RESERVE attribute when hot-remove are > > -executing-, their attribute should be changed. > > > > For example, how is like following dummy code? Is it impossible? > > (Not only here, some places will have to be modified..) > > Right, this should be possible. I was somewhat wandering from the subject, > because I noticed that there may be a bigger problem with MIGRATE_RESERVE > pages in ZONE_MOVABLE, and that we may not want to have them in the first > place. > > The more memory we add to ZONE_MOVABLE, the less reserved pages will > remain to the other zones. In setup_per_zone_pages_min(), min_free_kbytes > will be redistributed to a zone where the kernel cannot make any use of > it, effectively reducing the available min_free_kbytes. This just doesn't > sound right. I believe that a similar situation is the reason why highmem > pages are skipped in the calculation and I think that we need that for > ZONE_MOVABLE too. Any thoughts on that problem? > > Setting pages_min to 0 for ZONE_MOVABLE, while not capping pages_low > and pages_high, could be an option. I don't have a sufficient memory > managment overview to tell if that has negative side effects, maybe > someone with a deeper insight could comment on that.
At least, pages_min should not be 0. It is used as watermark when memory shortage situation. If it is 0, kernel will misunderstand shortage situation. Certainly, pages_min value may be not appropriate value for ZONE_MOVABLE. But it is not memory-hotplug issue.
True your question is why ZONE_MOVABLE has MIGRATE_RESREVE pages, right? However, I think it is intended for emergency pool of memory shortage situation for ZONE_MOVABLE via fallback[]. If not, these MIGRATE_RESERVE pages are not made originally. It is why I wrote previous mail.
Mel Gormal-san knows around here very well. He may explain its detail more.
Bye.
-- Yasunori Goto
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