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    SubjectRe: [PATCH] Make CONFIG_MIGRATION available for s390
    Gerald Schaefer wrote:

    > Index: linux-2.6/include/linux/migrate.h
    > ===================================================================
    > --- linux-2.6.orig/include/linux/migrate.h
    > +++ linux-2.6/include/linux/migrate.h
    > @@ -13,6 +13,7 @@ static inline int vma_migratable(struct
    > {
    > if (vma->vm_flags & (VM_IO|VM_HUGETLB|VM_PFNMAP|VM_RESERVED))
    > return 0;
    > +#ifdef CONFIG_NUMA
    > /*
    > * Migration allocates pages in the highest zone. If we cannot
    > * do so then migration (at least from node to node) is not
    > @@ -22,6 +23,7 @@ static inline int vma_migratable(struct
    > gfp_zone(mapping_gfp_mask(vma->vm_file->f_mapping))
    > < policy_zone)
    > return 0;
    > +#endif
    > return 1;
    > }

    This will extend the number of pages that are migratable and lead to strange
    semantics in the NUMA case. There suddenly vma_is migratable will forbid hotplug
    to migrate certain pages.

    I think we need two functions:

    vma_migratable() General migratability

    vma_policy_migratable() Migratable under NUMA policies.


    > Index: linux-2.6/include/linux/mm.h
    > ===================================================================
    > --- linux-2.6.orig/include/linux/mm.h
    > +++ linux-2.6/include/linux/mm.h
    > @@ -193,6 +193,8 @@ struct vm_operations_struct {
    > */
    > struct mempolicy *(*get_policy)(struct vm_area_struct *vma,
    > unsigned long addr);
    > +#endif
    > +#ifdef CONFIG_MIGRATION
    > int (*migrate)(struct vm_area_struct *vma, const nodemask_t *from,
    > const nodemask_t *to, unsigned long flags);
    > #endif

    That wont work since the migrate function takes a nodemask! The point of
    the function is to move memory from node to node which is something that you
    *cannot* do in a non NUMA configuration. So leave this chunk out.


    > Index: linux-2.6/mm/Kconfig
    > ===================================================================
    > --- linux-2.6.orig/mm/Kconfig
    > +++ linux-2.6/mm/Kconfig
    > @@ -174,7 +174,7 @@ config SPLIT_PTLOCK_CPUS
    > config MIGRATION
    > bool "Page migration"
    > def_bool y
    > - depends on NUMA
    > + depends on NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE
    > help
    > Allows the migration of the physical location of pages of processes
    > while the virtual addresses are not changed. This is useful for

    Hmmm... Okay. I tried to make MIGRATION as independent of CONFIG_NUMA as possible so hopefully this will work.





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