linux-kernel - [PATCHv4 19/43] brd: make it handle huge pages

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Date:   Tue, 25 Oct 2016 03:13:18 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     "Theodore Ts'o" <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Jan Kara <jack@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Hugh Dickins <hughd@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Matthew Wilcox <willy@...radead.org>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-block@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [PATCHv4 19/43] brd: make it handle huge pages

Do not assume length of bio segment is never larger than PAGE_SIZE.
With huge pages it's HPAGE_PMD_SIZE (2M on x86-64).

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
---
 drivers/block/brd.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/drivers/block/brd.c b/drivers/block/brd.c
index 0c76d4016eeb..4214163350d2 100644
--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -202,12 +202,15 @@ static int copy_to_brd_setup(struct brd_device *brd, sector_t sector, size_t n)
 	size_t copy;
 
 	copy = min_t(size_t, n, PAGE_SIZE - offset);
+	n -= copy;
 	if (!brd_insert_page(brd, sector))
 		return -ENOSPC;
-	if (copy < n) {
+	while (n) {
 		sector += copy >> SECTOR_SHIFT;
 		if (!brd_insert_page(brd, sector))
 			return -ENOSPC;
+		copy = min_t(size_t, n, PAGE_SIZE);
+		n -= copy;
 	}
 	return 0;
 }
@@ -242,6 +245,7 @@ static void copy_to_brd(struct brd_device *brd, const void *src,
 	size_t copy;
 
 	copy = min_t(size_t, n, PAGE_SIZE - offset);
+	n -= copy;
 	page = brd_lookup_page(brd, sector);
 	BUG_ON(!page);
 
@@ -249,10 +253,11 @@ static void copy_to_brd(struct brd_device *brd, const void *src,
 	memcpy(dst + offset, src, copy);
 	kunmap_atomic(dst);
 
-	if (copy < n) {
+	while (n) {
 		src += copy;
 		sector += copy >> SECTOR_SHIFT;
-		copy = n - copy;
+		copy = min_t(size_t, n, PAGE_SIZE);
+		n -= copy;
 		page = brd_lookup_page(brd, sector);
 		BUG_ON(!page);
 
@@ -274,6 +279,7 @@ static void copy_from_brd(void *dst, struct brd_device *brd,
 	size_t copy;
 
 	copy = min_t(size_t, n, PAGE_SIZE - offset);
+	n -= copy;
 	page = brd_lookup_page(brd, sector);
 	if (page) {
 		src = kmap_atomic(page);
@@ -282,10 +288,11 @@ static void copy_from_brd(void *dst, struct brd_device *brd,
 	} else
 		memset(dst, 0, copy);
 
-	if (copy < n) {
+	while (n) {
 		dst += copy;
 		sector += copy >> SECTOR_SHIFT;
-		copy = n - copy;
+		copy = min_t(size_t, n, PAGE_SIZE);
+		n -= copy;
 		page = brd_lookup_page(brd, sector);
 		if (page) {
 			src = kmap_atomic(page);
-- 
2.9.3