Re: [PATCH v2 2/7] mm/migrate: correct failure handling if!hugepage_migration_support()

[Joonsoo Kim]

On Tue, Dec 10, 2013 at 10:17:56AM +0800, Wanpeng Li wrote:
> Hi Joonsoo,
> On Mon, Dec 09, 2013 at 06:10:43PM +0900, Joonsoo Kim wrote:
> >We should remove the page from the list if we fail without ENOSYS,
> >since migrate_pages() consider error cases except -ENOMEM and -EAGAIN
> >as permanent failure and it assumes that the page would be removed from
> >the list. Without this patch, we could overcount number of failure.
> >
> >In addition, we should put back the new hugepage if
> >!hugepage_migration_support(). If not, we would leak hugepage memory.
> >
> >Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> >
> >diff --git a/mm/migrate.c b/mm/migrate.c
> >index c6ac87a..b1cfd01 100644
> >--- a/mm/migrate.c
> >+++ b/mm/migrate.c
> >@@ -1011,7 +1011,7 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
> > {
> > 	int rc = 0;
> > 	int *result = NULL;
> >-	struct page *new_hpage = get_new_page(hpage, private, &result);
> >+	struct page *new_hpage;
> > 	struct anon_vma *anon_vma = NULL;
> >
> > 	/*
> >@@ -1021,9 +1021,12 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
> > 	 * tables or check whether the hugepage is pmd-based or not before
> > 	 * kicking migration.
> > 	 */
> >-	if (!hugepage_migration_support(page_hstate(hpage)))
> >+	if (!hugepage_migration_support(page_hstate(hpage))) {
> >+		putback_active_hugepage(hpage);
> > 		return -ENOSYS;
> 
> The memory hotplug(do_migrate_range) and hwpoison(soft_offline_huge_page) callsets both 
> will call putback_movable_pages/putback_active_hugepage for -ENOSYS case.

Hello Wanpeng.

Yes, those callsite handle error case, but error case handling should be done
in unmap_and_move_huge_page(). It is mentioned on patch 1. If we defer to
remove the pages from the list, nr_failed can be overcounted.

Thanks.
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