From: Ming Lei <ming.lei@redhat.com>
Date: Tue, 18 Jun 2019 09:37:47 +0800
Subject: scsi: pmcraid: use sg helper to iterate over scatterlist
Patch-mainline: v5.3-rc1
Git-commit: 74eb7446eda5e348dbb90981e91e9caf54f2fde4
References: bsc#1135990 jsc#SLE-4709

Unlike the legacy I/O path, scsi-mq preallocates a large array to hold
the scatterlist for each request. This static allocation can consume
substantial amounts of memory on modern controllers which support a
large number of concurrently outstanding requests.

To facilitate a switch to a smaller static allocation combined with a
dynamic allocation for requests that need it, we need to make sure all
SCSI drivers handle chained scatterlists correctly.

Convert remaining drivers that directly dereference the scatterlist
array to using the iterator functions.

[mkp: clarified commit message]

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Acked-by: Daniel Wagner <dwagner@suse.de>
---
 drivers/scsi/pmcraid.c |   14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

--- a/drivers/scsi/pmcraid.c
+++ b/drivers/scsi/pmcraid.c
@@ -3312,7 +3312,7 @@ static int pmcraid_copy_sglist(
 	int direction
 )
 {
-	struct scatterlist *scatterlist;
+	struct scatterlist *sg;
 	void *kaddr;
 	int bsize_elem;
 	int i;
@@ -3321,10 +3321,10 @@ static int pmcraid_copy_sglist(
 	/* Determine the actual number of bytes per element */
 	bsize_elem = PAGE_SIZE * (1 << sglist->order);
 
-	scatterlist = sglist->scatterlist;
+	sg = sglist->scatterlist;
 
-	for (i = 0; i < (len / bsize_elem); i++, buffer += bsize_elem) {
-		struct page *page = sg_page(&scatterlist[i]);
+	for (i = 0; i < (len / bsize_elem); i++, sg = sg_next(sg), buffer += bsize_elem) {
+		struct page *page = sg_page(sg);
 
 		kaddr = kmap(page);
 		if (direction == DMA_TO_DEVICE)
@@ -3339,11 +3339,11 @@ static int pmcraid_copy_sglist(
 			return -EFAULT;
 		}
 
-		scatterlist[i].length = bsize_elem;
+		sg->length = bsize_elem;
 	}
 
 	if (len % bsize_elem) {
-		struct page *page = sg_page(&scatterlist[i]);
+		struct page *page = sg_page(sg);
 
 		kaddr = kmap(page);
 
@@ -3354,7 +3354,7 @@ static int pmcraid_copy_sglist(
 
 		kunmap(page);
 
-		scatterlist[i].length = len % bsize_elem;
+		sg->length = len % bsize_elem;
 	}
 
 	if (rc) {