[PATCH v6 7/7] udmabuf: reuse folio array when pin folios

[Huan Yang]

When invoke memfd_pin_folios, we need offer an array to save each folio
which we pinned.

The currently way is dynamic alloc an array, get folios, save into
udmabuf and then free.

If the size is tiny(alloc from slab) is ok due to slab can cache it.
Or, just PCP order can cover, also ok.

But if size is huge, need fallback into vmalloc, then, not well, due to
each page need alloc, and map into vmalloc area. Too heavy.

Now that we need to iter each udmabuf item, then pin it's range folios,
we can reuse the maximum size range's folios array.

Signed-off-by: Huan Yang <link@xxxxxxxx>
Acked-by: Vivek Kasireddy <vivek.kasireddy@xxxxxxxxx>
---
 drivers/dma-buf/udmabuf.c | 36 +++++++++++++++++++++---------------
 1 file changed, 21 insertions(+), 15 deletions(-)

diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
index 0e405a589ca2..9fc5d22d54ae 100644
--- a/drivers/dma-buf/udmabuf.c
+++ b/drivers/dma-buf/udmabuf.c
@@ -341,28 +341,20 @@ static int export_udmabuf(struct udmabuf *ubuf,
 }
 
 static long udmabuf_pin_folios(struct udmabuf *ubuf, struct file *memfd,
-			       loff_t start, loff_t size)
+			       loff_t start, loff_t size, struct folio **folios)
 {
 	pgoff_t nr_pinned = ubuf->nr_pinned;
 	pgoff_t upgcnt = ubuf->pagecount;
-	struct folio **folios = NULL;
 	u32 cur_folio, cur_pgcnt;
 	pgoff_t pgoff, pgcnt;
 	long nr_folios;
-	long ret = 0;
 	loff_t end;
 
 	pgcnt = size >> PAGE_SHIFT;
-	folios = kvmalloc_array(pgcnt, sizeof(*folios), GFP_KERNEL);
-	if (!folios)
-		return -ENOMEM;
-
 	end = start + (pgcnt << PAGE_SHIFT) - 1;
 	nr_folios = memfd_pin_folios(memfd, start, end, folios, pgcnt, &pgoff);
-	if (nr_folios <= 0) {
-		ret = nr_folios ? nr_folios : -EINVAL;
-		goto end;
-	}
+	if (nr_folios <= 0)
+		return nr_folios ? nr_folios : -EINVAL;
 
 	cur_pgcnt = 0;
 	for (cur_folio = 0; cur_folio < nr_folios; ++cur_folio) {
@@ -391,14 +383,15 @@ static long udmabuf_pin_folios(struct udmabuf *ubuf, struct file *memfd,
 end:
 	ubuf->pagecount = upgcnt;
 	ubuf->nr_pinned = nr_pinned;
-	kvfree(folios);
-	return ret;
+	return 0;
 }
 
 static long udmabuf_create(struct miscdevice *device,
 			   struct udmabuf_create_list *head,
 			   struct udmabuf_create_item *list)
 {
+	unsigned long max_nr_folios = 0;
+	struct folio **folios = NULL;
 	pgoff_t pgcnt = 0, pglimit;
 	struct udmabuf *ubuf;
 	long ret = -EINVAL;
@@ -410,14 +403,19 @@ static long udmabuf_create(struct miscdevice *device,
 
 	pglimit = (size_limit_mb * 1024 * 1024) >> PAGE_SHIFT;
 	for (i = 0; i < head->count; i++) {
+		pgoff_t subpgcnt;
+
 		if (!PAGE_ALIGNED(list[i].offset))
 			goto err_noinit;
 		if (!PAGE_ALIGNED(list[i].size))
 			goto err_noinit;
 
-		pgcnt += list[i].size >> PAGE_SHIFT;
+		subpgcnt = list[i].size >> PAGE_SHIFT;
+		pgcnt += subpgcnt;
 		if (pgcnt > pglimit)
 			goto err_noinit;
+
+		max_nr_folios = max_t(unsigned long, subpgcnt, max_nr_folios);
 	}
 
 	if (!pgcnt)
@@ -427,6 +425,12 @@ static long udmabuf_create(struct miscdevice *device,
 	if (ret)
 		goto err;
 
+	folios = kvmalloc_array(max_nr_folios, sizeof(*folios), GFP_KERNEL);
+	if (!folios) {
+		ret = -ENOMEM;
+		goto err;
+	}
+
 	for (i = 0; i < head->count; i++) {
 		struct file *memfd = fget(list[i].memfd);
 
@@ -442,7 +446,7 @@ static long udmabuf_create(struct miscdevice *device,
 		}
 
 		ret = udmabuf_pin_folios(ubuf, memfd, list[i].offset,
-					 list[i].size);
+					 list[i].size, folios);
 		fput(memfd);
 		if (ret)
 			goto err;
@@ -453,12 +457,14 @@ static long udmabuf_create(struct miscdevice *device,
 	if (ret < 0)
 		goto err;
 
+	kvfree(folios);
 	return ret;
 
 err:
 	deinit_udmabuf(ubuf);
 err_noinit:
 	kfree(ubuf);
+	kvfree(folios);
 	return ret;
 }
 
-- 
2.45.2