On 1/9/22 20:23, Matthew Wilcox (Oracle) wrote:
Simplify try_grab_compound_head() and remove an unnecessary
VM_BUG_ON by handling pages both with and without a pincount field in
page_pincount_add().
Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
mm/gup.c | 33 +++++++++++++++------------------
1 file changed, 15 insertions(+), 18 deletions(-)
Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx>
thanks,
--
John Hubbard
NVIDIA
diff --git a/mm/gup.c b/mm/gup.c
index dbb1b54d0def..3ed9907f3c8d 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -29,12 +29,23 @@ struct follow_page_context {
unsigned int page_mask;
};
-static void hpage_pincount_add(struct page *page, int refs)
+/*
+ * When pinning a compound page of order > 1 (which is what
+ * hpage_pincount_available() checks for), use an exact count to track
+ * it, via page_pincount_add/_sub().
+ *
+ * However, be sure to *also* increment the normal page refcount field
+ * at least once, so that the page really is pinned. That's why the
+ * refcount from the earlier try_get_compound_head() is left intact.
+ */
+static void page_pincount_add(struct page *page, int refs)
{
- VM_BUG_ON_PAGE(!hpage_pincount_available(page), page);
VM_BUG_ON_PAGE(page != compound_head(page), page);
- atomic_add(refs, compound_pincount_ptr(page));
+ if (hpage_pincount_available(page))
+ atomic_add(refs, compound_pincount_ptr(page));
+ else
+ page_ref_add(page, refs * (GUP_PIN_COUNTING_BIAS - 1));
}
static void hpage_pincount_sub(struct page *page, int refs)
@@ -150,21 +161,7 @@ struct page *try_grab_compound_head(struct page *page,
if (!page)
return NULL;
- /*
- * When pinning a compound page of order > 1 (which is what
- * hpage_pincount_available() checks for), use an exact count to
- * track it, via hpage_pincount_add/_sub().
- *
- * However, be sure to *also* increment the normal page refcount
- * field at least once, so that the page really is pinned.
- * That's why the refcount from the earlier
- * try_get_compound_head() is left intact.
- */
- if (hpage_pincount_available(page))
- hpage_pincount_add(page, refs);
- else
- page_ref_add(page, refs * (GUP_PIN_COUNTING_BIAS - 1));
-
+ page_pincount_add(page, refs);
mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_ACQUIRED,
refs);
