Re: [PATCH 5/6] mm: migrate: don't split THP for misplaced NUMA page
From: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Date: 2021-03-30 14:44:08
Also in:
linux-s390, lkml
On Mon, 29 Mar 2021 11:33:11 -0700 Yang Shi [off-list ref] wrote:
quoted hunk ↗ jump to hunk
The old behavior didn't split THP if migration is failed due to lack of memory on the target node. But the THP migration does split THP, so keep the old behavior for misplaced NUMA page migration. Signed-off-by: Yang Shi <redacted> --- mm/migrate.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)diff --git a/mm/migrate.c b/mm/migrate.c index 86325c750c14..1c0c873375ab 100644 --- a/mm/migrate.c +++ b/mm/migrate.c@@ -1444,6 +1444,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page, int swapwrite = current->flags & PF_SWAPWRITE; int rc, nr_subpages; LIST_HEAD(ret_pages); + bool nosplit = (reason == MR_NUMA_MISPLACED); if (!swapwrite) current->flags |= PF_SWAPWRITE;@@ -1495,7 +1496,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page, */ case -ENOSYS: /* THP migration is unsupported */ - if (is_thp) { + if (is_thp && !nosplit) {
This is the "THP migration is unsupported" case, but according to your description you rather want to change the -ENOMEM case? Could this be the correct place to trigger THP split for NUMA balancing, for architectures not supporting THP migration, like s390? Do I understand it correctly that this change (for -ENOSYS) would result in always failed THP migrations during NUMA balancing, if THP migration was not supported?