Messages in this thread Patch in this message | | | Subject | Re: memory hotplug: hot-remove fails on lowest chunk in ZONE_MOVABLE | From | Gerald Schaefer <> | Date | Tue, 29 Jul 2008 18:07:33 +0200 |
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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?
Thanks, Gerald
--- include/linux/mmzone.h | 5 +++++ mm/page_alloc.c | 4 ++-- 2 files changed, 7 insertions(+), 2 deletions(-)
Index: linux-2.6/include/linux/mmzone.h =================================================================== --- linux-2.6.orig/include/linux/mmzone.h +++ linux-2.6/include/linux/mmzone.h @@ -660,6 +660,11 @@ static inline int is_dma(struct zone *zo #endif } +static inline int is_movable(struct zone *zone) +{ + return zone == zone->zone_pgdat->node_zones + ZONE_MOVABLE; +} + /* These two functions are used to setup the per zone pages min values */ struct ctl_table; struct file; Index: linux-2.6/mm/page_alloc.c =================================================================== --- linux-2.6.orig/mm/page_alloc.c +++ linux-2.6/mm/page_alloc.c @@ -4210,7 +4210,7 @@ void setup_per_zone_pages_min(void) /* Calculate total number of !ZONE_HIGHMEM pages */ for_each_zone(zone) { - if (!is_highmem(zone)) + if (!is_highmem(zone) && !is_movable(zone)) lowmem_pages += zone->present_pages; } @@ -4243,7 +4243,7 @@ void setup_per_zone_pages_min(void) * If it's a lowmem zone, reserve a number of pages * proportionate to the zone's size. */ - zone->pages_min = tmp; + zone->pages_min = is_movable(zone) ? 0 : tmp; } zone->pages_low = zone->pages_min + (tmp >> 2);
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