mm/hugetlb: make hugetlb_reserve_pages() return nr of entries updated

Patch series "mm/memfd: Reserve hugetlb folios before allocation", v4.

There are cases when we try to pin a folio but discover that it has not
been faulted-in.  So, we try to allocate it in memfd_alloc_folio() but the
allocation request may not succeed if there are no active reservations in
the system at that instant.

Therefore, making a reservation (by calling hugetlb_reserve_pages())
associated with the allocation will ensure that our request would not fail
due to lack of reservations.  This will also ensure that proper
region/subpool accounting is done with our allocation.


This patch (of 3):

Currently, hugetlb_reserve_pages() returns a bool to indicate whether the
reservation map update for the range [from, to] was successful or not. 
This is not sufficient for the case where the caller needs to determine
how many entries were updated for the range.

Therefore, have hugetlb_reserve_pages() return the number of entries
updated in the reservation map associated with the range [from, to]. 
Also, update the callers of hugetlb_reserve_pages() to handle the new
return value.

Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Vivek Kasireddy <[email protected]>
Cc: Steve Sistare <[email protected]>
Cc: Muchun Song <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Gerd Hoffmann <[email protected]>
Cc: Oscar Salvador <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

1 files changed, 13 insertions, 6 deletions

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index c7ba95030241..e1570735012a 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -7244,8 +7244,15 @@ long hugetlb_change_protection(struct vm_area_struct *vma,
 	return pages > 0 ? (pages << h->order) : pages;
 }
 
-/* Return true if reservation was successful, false otherwise.  */
-bool hugetlb_reserve_pages(struct inode *inode,
+/*
+ * Update the reservation map for the range [from, to].
+ *
+ * Returns the number of entries that would be added to the reservation map
+ * associated with the range [from, to].  This number is greater or equal to
+ * zero. -EINVAL or -ENOMEM is returned in case of any errors.
+ */
+
+long hugetlb_reserve_pages(struct inode *inode,
 					long from, long to,
 					struct vm_area_struct *vma,
 					vm_flags_t vm_flags)
@@ -7260,7 +7267,7 @@ bool hugetlb_reserve_pages(struct inode *inode,
 	/* This should never happen */
 	if (from > to) {
 		VM_WARN(1, "%s called with a negative range\n", __func__);
-		return false;
+		return -EINVAL;
 	}
 
 	/*
@@ -7275,7 +7282,7 @@ bool hugetlb_reserve_pages(struct inode *inode,
 	 * without using reserves
 	 */
 	if (vm_flags & VM_NORESERVE)
-		return true;
+		return 0;
 
 	/*
 	 * Shared mappings base their reservation on the number of pages that
@@ -7382,7 +7389,7 @@ bool hugetlb_reserve_pages(struct inode *inode,
 			hugetlb_cgroup_put_rsvd_cgroup(h_cg);
 		}
 	}
-	return true;
+	return chg;
 
 out_put_pages:
 	spool_resv = chg - gbl_reserve;
@@ -7410,7 +7417,7 @@ out_err:
 		kref_put(&resv_map->refs, resv_map_release);
 		set_vma_resv_map(vma, NULL);
 	}
-	return false;
+	return chg < 0 ? chg : add < 0 ? add : -EINVAL;
 }
 
 long hugetlb_unreserve_pages(struct inode *inode, long start, long end,