On Thu, 14 Jul 2016, Xishi Qiu wrote: > alloc_migrate_target() is called from migrate_pages(), and the page > is always from user space, so we can add __GFP_HIGHMEM directly. > > Second, when we offline a node, the new page should alloced from other > nodes instead of the current node, because re-migrate is a waste of > time. >
alloc_migrate_target() is not only used from memory hotplug, it is also used for CMA: we won't be isolating PageHuge() pages in isolate_migratepages_range(), so this would cause a regression where we'd be migrating memory to a remote NUMA node rather than preferring to allocate locally. You may find it useful to use the 'private' field of the migrate_pages() callback to specify the node the page should preferably be migrated to. > Signed-off-by: Xishi Qiu <[email protected]> > --- > mm/page_isolation.c | 16 ++++++---------- > 1 file changed, 6 insertions(+), 10 deletions(-) > > diff --git a/mm/page_isolation.c b/mm/page_isolation.c > index 612122b..83848dc 100644 > --- a/mm/page_isolation.c > +++ b/mm/page_isolation.c > @@ -282,20 +282,16 @@ int test_pages_isolated(unsigned long start_pfn, > unsigned long end_pfn, > struct page *alloc_migrate_target(struct page *page, unsigned long private, > int **resultp) > { > - gfp_t gfp_mask = GFP_USER | __GFP_MOVABLE; > - > /* > - * TODO: allocate a destination hugepage from a nearest neighbor node, > + * TODO: allocate a destination page from a nearest neighbor node, > * accordance with memory policy of the user process if possible. For > * now as a simple work-around, we use the next node for destination. > */ > + int nid = next_node_in(page_to_nid(page), node_online_map); > + > if (PageHuge(page)) > return alloc_huge_page_node(page_hstate(compound_head(page)), > - next_node_in(page_to_nid(page), > - node_online_map)); > - > - if (PageHighMem(page)) > - gfp_mask |= __GFP_HIGHMEM; > - > - return alloc_page(gfp_mask); > + nid); > + else > + return __alloc_pages_node(nid, GFP_HIGHUSER_MOVABLE, 0); I don't think this __alloc_pages_node() does what you think it does, it only prefers nid here and will readily fallback to other nodes if necessary. That is different than alloc_huge_page_node() which does no fallback. So there's two issues with this change: (1) inconsistency between PageHuge() and !PageHuge() behavior, and (2) the use of __alloc_pages_node() does not match the commit description which states "re-migrate is a waste of time."
