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    SubjectRe: [PATCH 3/7] Allow CONFIG_MIGRATION to be set without CONFIG_NUMA
    On Tue, 29 May 2007, Mel Gorman wrote:

    > CONFIG_MIGRATION currently depends on CONFIG_NUMA. move_pages() is the only
    > user of migration today and as this system call is only meaningful on NUMA,
    > it makes sense. However, memory compaction will operate within a zone and is
    > useful on both NUMA and non-NUMA systems. This patch allows CONFIG_MIGRATION
    > to be used in all memory models. To preserve existing behaviour, move_pages()
    > is only available when CONFIG_NUMA is set.

    Hmmm... I thought I had this already set up so that it would be easy to
    switch page migration to not depend on CONFIG_NUMA. Not so it seems.

    > --- linux-2.6.22-rc2-mm1-005_migrate_nocontext/include/linux/migrate.h 2007-05-28 14:11:32.000000000 +0100
    > +++ linux-2.6.22-rc2-mm1-015_migration_flatmem/include/linux/migrate.h 2007-05-29 10:00:09.000000000 +0100
    > @@ -7,7 +7,7 @@
    >
    > typedef struct page *new_page_t(struct page *, unsigned long private, int **);
    >
    > -#ifdef CONFIG_MIGRATION
    > +#ifdef CONFIG_SYSCALL_MOVE_PAGES
    > /* Check if a vma is migratable */
    > static inline int vma_migratable(struct vm_area_struct *vma)
    > {
    > @@ -24,7 +24,14 @@ static inline int vma_migratable(struct
    > return 0;
    > return 1;
    > }
    > +#else
    > +static inline int vma_migratable(struct vm_area_struct *vma)
    > +{
    > + return 0;
    > +}
    > +#endif

    I guess we get compilation failures because of the reference to
    policy_zone here for the !NUMA case? I think vma migratable is not used at
    all if !NUMA.


    > +#ifdef CONFIG_MIGRATION
    > extern int isolate_lru_page(struct page *p, struct list_head *pagelist);
    > extern int putback_lru_pages(struct list_head *l);
    > extern int migrate_page(struct address_space *,
    > @@ -40,8 +47,6 @@ extern int migrate_vmas(struct mm_struct
    > const nodemask_t *from, const nodemask_t *to,
    > unsigned long flags);
    > #else
    > -static inline int vma_migratable(struct vm_area_struct *vma)
    > - { return 0; }

    Maybe this block is not necessary?

    > diff -rup -X /usr/src/patchset-0.6/bin//dontdiff linux-2.6.22-rc2-mm1-005_migrate_nocontext/include/linux/mm.h linux-2.6.22-rc2-mm1-015_migration_flatmem/include/linux/mm.h
    > --- linux-2.6.22-rc2-mm1-005_migrate_nocontext/include/linux/mm.h 2007-05-24 10:13:34.000000000 +0100
    > +++ linux-2.6.22-rc2-mm1-015_migration_flatmem/include/linux/mm.h 2007-05-28 14:13:44.000000000 +0100
    > @@ -242,6 +242,8 @@ struct vm_operations_struct {
    > int (*set_policy)(struct vm_area_struct *vma, struct mempolicy *new);
    > struct mempolicy *(*get_policy)(struct vm_area_struct *vma,
    > unsigned long addr);
    > +#endif /* CONFIG_NUMA */
    > +#ifdef CONFIG_MIGRATION
    > int (*migrate)(struct vm_area_struct *vma, const nodemask_t *from,
    > const nodemask_t *to, unsigned long flags);
    > #endif

    Correct.

    > diff -rup -X /usr/src/patchset-0.6/bin//dontdiff linux-2.6.22-rc2-mm1-005_migrate_nocontext/mm/Kconfig linux-2.6.22-rc2-mm1-015_migration_flatmem/mm/Kconfig
    > --- linux-2.6.22-rc2-mm1-005_migrate_nocontext/mm/Kconfig 2007-05-24 10:13:34.000000000 +0100
    > +++ linux-2.6.22-rc2-mm1-015_migration_flatmem/mm/Kconfig 2007-05-29 09:57:23.000000000 +0100
    > @@ -145,13 +145,16 @@ config SPLIT_PTLOCK_CPUS
    > config MIGRATION
    > bool "Page migration"
    > def_bool y
    > - depends on NUMA
    > help
    > Allows the migration of the physical location of pages of processes
    > while the virtual addresses are not changed. This is useful for
    > example on NUMA systems to put pages nearer to the processors accessing
    > the page.
    >
    > +config SYSCALL_MOVE_PAGES
    > + def_bool y
    > + depends on MIGRATION && NUMA
    > +

    Do we really need the CONFIG_SYSCALL_MOVE_PAGES? I think you will directly
    access the lower levels. So why have it? CONFIG_SYSCALL_MOVE_PAGES ==
    CONFIG_NUMA.
    -
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