Messages in this thread Patch in this message | | | Date | Wed, 30 Jul 2008 12:16:52 +0900 | From | Yasunori Goto <> | Subject | Re: memory hotplug: hot-remove fails on lowest chunk in ZONE_MOVABLE |
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> On Wed, 2008-07-23 at 11:48 +0900, Yasunori Goto wrote: > > > Memory hot-remove of the lowest memory chunk in ZONE_MOVABLE will fail > > > because of some reserved pages at the beginning of each zone > > > (MIGRATE_RESERVED). > > > > > I believe you are right. Current hot-remove code is NOT perfect. > > You may remove some sections, but may not other sections, > > because there are some un-removable pages by some reasons > > (not only MIGRATE_RESERVED). > > > > I think MIGRATE_RESERVED pages should be move to MIGRATE_MOVABLE when > > those pages must be removed, and should recalculate MIGRATE_RESERVED pages. > > Hi, > > Would it be an option to set pages_min to 0 for ZONE_MOVABLE in > setup_per_zone_pages_min()? This would avoid the MIGRATE_RESERVED vs. > MIGRATE_MOVABLE conflict on memory hot-remove. If I understand it > correctly, the kernel wouldn't be able to use the reserved pages in > ZONE_MOVABLE for __GFP_HIGH and PF_MEMALLOC allocations anyway, right? > > At the moment, ZONE_MOVABLE pages will also account for the lowmem_pages > calculation in setup_per_zone_pages_min(). The recalculation will then > redistribute and reduce the amount of reserved pages for the other zones. > Won't this effectively reduce the amount of reserved min_free_kbytes memory > that is available to the kernel, even getting worse the more memory is > added to ZONE_MOVABLE? > > With the following patch, ZONE_MOVABLE will be skipped for the > lowmem_pages calculation, just like it is already done for highmem. > It will also set pages_min to 0 for ZONE_MOVABLE. But I have an uneasy > feeling about this, because I may be missing side effects from this. > Any opinions?
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..)
Thanks.
--- mm/page_alloc.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
Index: current/mm/page_alloc.c =================================================================== --- current.orig/mm/page_alloc.c 2008-07-29 22:17:54.000000000 +0900 +++ current/mm/page_alloc.c 2008-07-30 12:04:03.000000000 +0900 @@ -4828,7 +4828,9 @@ int set_migratetype_isolate(struct page /* * In future, more migrate types will be able to be isolation target. */ - if (get_pageblock_migratetype(page) != MIGRATE_MOVABLE) + if ((get_pageblock_migratetype(page) != MIGRATE_MOVABLE) || + !((removing section is the last section on the zone) && + get_pageblock_migratetype(page) == MIGRATE_RESREVE)) goto out; set_pageblock_migratetype(page, MIGRATE_ISOLATE); move_freepages_block(zone, page, MIGRATE_ISOLATE);
-- Yasunori Goto
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