Re: [PATCH] mm/gup.c: Simplify and fix check_and_migrate_movable_pages() return codes

John Hubbard
2022-07-29T21:22:11Z

On 7/29/22 12:44, Jason Gunthorpe wrote:

> I came up with this ontop:
>
That cleans it up even more, looks nice. I'd go just a touch further,
and also (unless there is some odd reason?) stay with -EAGAIN rather
than -EBUSY, because otherwise both the function's comment header, and
the caller, should change from -EBUSY to -EAGAIN just for consistency.

And also because the way it's used: the caller is literally "trying
again".

So on top of the ontop:

diff --git a/mm/gup.c b/mm/gup.c
index 43c1fc532842..5f04033ee0ed 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1901,10 +1901,12 @@ struct page *get_dump_page(unsigned long addr)

#ifdef CONFIG_MIGRATION
/*
- * Check whether all pages are pinnable. If some pages are not pinnable migrate
- * them and unpin all the pages. Returns -EAGAIN if pages were unpinned or zero
- * if all pages are pinnable and in the right zone. Other errors indicate
- * migration failure.
+ * Check whether all pages are pinnable. If some pages are not pinnable, migrate
+ * them and unpin all the pages.
+ * Return values:
+ * 0: all pages are already pinnable and in the right zone
+ * -EAGAIN: some pages were unpinned or were zero
+ * -ENOMEM: migration of some pages failed
*/
static long check_and_migrate_movable_pages(unsigned long nr_pages,
struct page **pages,
@@ -1914,11 +1916,11 @@ static long check_and_migrate_movable_pages(unsigned long nr_pages,
.nid = NUMA_NO_NODE,
.gfp_mask = GFP_USER | __GFP_NOWARN,
};
- unsigned long i;
+ unsigned long i, not_migrated;
struct folio *prev_folio = NULL;
LIST_HEAD(movable_page_list);
bool drain_allow = true, coherent_pages = false;
- int ret = -EBUSY;
+ int ret = -EAGAIN;

for (i = 0; i < nr_pages; i++) {
struct folio *folio = page_folio(pages[i]);
@@ -1990,7 +1992,7 @@ static long check_and_migrate_movable_pages(unsigned long nr_pages,

/*
* Unpin all pages. If device coherent pages were found
- * migrate_deivce_coherent_page() will have dropped the pin and set
+ * migrate_device_coherent_page() will have dropped the pin and set
* pages[i] == NULL.
*/
for (i = 0; i < nr_pages; i++) {

thanks,
--
John Hubbard
NVIDIA