Re: [PATCH] mm,migration: Avoid race between shift_arg_pages() andrmap_walk() during migration by not migrating temporary stacks

[Christoph Lameter]

Still think this special casing is not that good.

One can also disable migration by providing a migration function that
always fails. One such function exists in mm/migrate.c:

/* Always fail migration. Used for mappings that are not movable */
int fail_migrate_page(struct address_space *mapping,
                        struct page *newpage, struct page *page)
{
        return -EIO;
}
EXPORT_SYMBOL(fail_migrate_page);


The migration function is specified in

vma->vm_ops->migrate

If that is set to fail_migrate_page() then the pages in the vma will never
be migrated. XFS uses it f.e. to avoid page migration:

STATIC int
xfs_mapping_buftarg(
        xfs_buftarg_t           *btp,
        struct block_device     *bdev)
{
        struct backing_dev_info *bdi;
        struct inode            *inode;
        struct address_space    *mapping;
        static const struct address_space_operations mapping_aops = {
                .sync_page = block_sync_page,
                .migratepage = fail_migrate_page,
        };



Would it not be possible to do something similar for the temporary stack?
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