[PATCH 3/6] Introduce blk_max_segment()

Kent Overstreet
2013-09-25T20:22:59Z

From: Kent Overstreet <koverstreet@google.com>

Signed-off-by: Kent Overstreet <kmo@daterainc.com>
---
arch/x86/include/asm/io.h | 3 +++
block/blk-merge.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++
drivers/xen/biomerge.c | 8 ++++++++
include/linux/blkdev.h | 1 +
4 files changed, 63 insertions(+)

diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
index 34f69cb..4799845 100644
--- a/arch/x86/include/asm/io.h
+++ b/arch/x86/include/asm/io.h
@@ -335,6 +335,9 @@ extern bool is_early_ioremap_ptep(pte_t *ptep);
#include <xen/xen.h>
struct bio_vec;

+extern bool xen_page_phys_mergeable(const struct page *p1,
+ const struct page *p2);
+
extern bool xen_biovec_phys_mergeable(const struct bio_vec *vec1,
const struct bio_vec *vec2);

diff --git a/block/blk-merge.c b/block/blk-merge.c
index 7cebf46..c9c837b 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -9,6 +9,57 @@

#include "blk.h"

+static unsigned int __blk_max_segment(struct request_queue *q, struct bio_vec *bv)
+{
+ unsigned len = bv->bv_len;
+
+ len = min_t(unsigned, len, blk_queue_cluster(q)
+ ? queue_max_segment_size(q)
+ : PAGE_SIZE);
+
+ len = min_t(unsigned, len,
+ queue_segment_boundary(q) + 1 -
+ (bvec_to_phys(bv) & queue_segment_boundary(q)));
+
+ return len;
+}
+
+#ifdef CONFIG_XEN
+unsigned int blk_max_segment(struct request_queue *q, struct bio_vec *bv)
+{
+ unsigned len = __blk_max_segment(q, bv);
+ unsigned ret;
+ struct page *next, *prev;
+
+ if (!xen_domain())
+ return len;
+
+ ret = min_t(unsigned, len, PAGE_SIZE - bv->bv_offset);
+ prev = bv->bv_page;
+
+ while (ret < len) {
+ next = nth_page(prev, 1);
+
+ if (!xen_page_phys_mergeable(prev, next))
+ break;
+
+ ret += min_t(unsigned, len - ret, PAGE_SIZE);
+ prev = next;
+ }
+
+ return ret;
+}
+
+#else
+
+unsigned int blk_max_segment(struct request_queue *q, struct bio_vec *bv)
+{
+ return __blk_max_segment(q, bv);
+}
+
+#endif
+EXPORT_SYMBOL(blk_max_segment);
+
static struct bio *blk_bio_discard_split(struct request_queue *q,
struct bio *bio,
struct bio_set *bs)
diff --git a/drivers/xen/biomerge.c b/drivers/xen/biomerge.c
index 0edb91c..d9fb598 100644
--- a/drivers/xen/biomerge.c
+++ b/drivers/xen/biomerge.c
@@ -3,6 +3,14 @@
#include <linux/export.h>
#include <xen/page.h>

+bool xen_page_phys_mergeable(const struct page *p1, const struct page *p2)
+{
+ unsigned long mfn1 = pfn_to_mfn(page_to_pfn(p1));
+ unsigned long mfn2 = pfn_to_mfn(page_to_pfn(p2));
+
+ return mfn1 + 1 == mfn2;
+}
+
bool xen_biovec_phys_mergeable(const struct bio_vec *vec1,
const struct bio_vec *vec2)
{
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 1afe1bb..4a45e35 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -746,6 +746,7 @@ extern void blk_rq_unprep_clone(struct request *rq);
extern int blk_insert_cloned_request(struct request_queue *q,
struct request *rq);
extern void blk_delay_queue(struct request_queue *, unsigned long);
+extern unsigned int blk_max_segment(struct request_queue *, struct bio_vec *);
extern void blk_recount_segments(struct request_queue *, struct bio *);
extern int scsi_verify_blk_ioctl(struct block_device *, unsigned int);
extern int scsi_cmd_blk_ioctl(struct block_device *, fmode_t,
--
1.8.4.rc3