Re: [Cluster-devel] [PATCH V12 03/20] block: remove the "cluster" flag

[Omar Sandoval]

On Mon, Nov 26, 2018 at 10:17:03AM +0800, Ming Lei wrote:
> From: Christoph Hellwig 
> 
> The cluster flag implements some very old SCSI behavior.  As far as I
> can tell the original intent was to enable or disable any kind of
> segment merging.  But the actually visible effect to the LLDD is that
> it limits each segments to be inside a single page, which we can
> also affect by setting the maximum segment size and the segment
> boundary.

Reviewed-by: Omar Sandoval 

One comment typo below.

> Signed-off-by: Christoph Hellwig 
> 
> Replace virt boundary with segment boundary limit.
> 
> Signed-off-by: Ming Lei 
> ---
>  block/blk-merge.c   | 20 
>  block/blk-settings.c|  3 ---
>  block/blk-sysfs.c   |  5 +
>  drivers/scsi/scsi_lib.c | 20 
>  include/linux/blkdev.h  |  6 --
>  5 files changed, 25 insertions(+), 29 deletions(-)
> 

[snip]

> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index 0df15cb738d2..78d6d05992b0 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -1810,6 +1810,8 @@ static int scsi_map_queues(struct blk_mq_tag_set *set)
>  void __scsi_init_queue(struct Scsi_Host *shost, struct request_queue *q)
>  {
>   struct device *dev = shost->dma_dev;
> + unsigned max_segment_size = dma_get_max_seg_size(dev);
> + unsigned long segment_boundary = shost->dma_boundary;
>  
>   /*
>* this limit is imposed by hardware restrictions
> @@ -1828,13 +1830,23 @@ void __scsi_init_queue(struct Scsi_Host *shost, 
> struct request_queue *q)
>   blk_queue_max_hw_sectors(q, shost->max_sectors);
>   if (shost->unchecked_isa_dma)
>   blk_queue_bounce_limit(q, BLK_BOUNCE_ISA);
> - blk_queue_segment_boundary(q, shost->dma_boundary);
>   dma_set_seg_boundary(dev, shost->dma_boundary);
>  
> - blk_queue_max_segment_size(q, dma_get_max_seg_size(dev));
> + /*
> +  * Clustering is a really old concept from the stone age of Linux
> +  * SCSI support.  But the basic idea is that we never give the
> +  * driver a segment that spans multiple pages.  For that we need
> +  * to limit the segment size, and set the segment boundary so that
> +  * we never merge a second segment which is no page aligned.

Typo, "which is not page aligned".

[Cluster-devel] [PATCH V12 03/20] block: remove the "cluster" flag

[Ming Lei]

From: Christoph Hellwig 

The cluster flag implements some very old SCSI behavior.  As far as I
can tell the original intent was to enable or disable any kind of
segment merging.  But the actually visible effect to the LLDD is that
it limits each segments to be inside a single page, which we can
also affect by setting the maximum segment size and the segment
boundary.

Signed-off-by: Christoph Hellwig 

Replace virt boundary with segment boundary limit.

Signed-off-by: Ming Lei 
---
 block/blk-merge.c   | 20 
 block/blk-settings.c|  3 ---
 block/blk-sysfs.c   |  5 +
 drivers/scsi/scsi_lib.c | 20 
 include/linux/blkdev.h  |  6 --
 5 files changed, 25 insertions(+), 29 deletions(-)

diff --git a/block/blk-merge.c b/block/blk-merge.c
index 6be04ef8da5b..e69d8f8ba819 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -195,7 +195,7 @@ static struct bio *blk_bio_segment_split(struct 
request_queue *q,
goto split;
}
 
-   if (bvprvp && blk_queue_cluster(q)) {
+   if (bvprvp) {
if (seg_size + bv.bv_len > queue_max_segment_size(q))
goto new_segment;
if (!biovec_phys_mergeable(q, bvprvp, ))
@@ -295,10 +295,10 @@ static unsigned int __blk_recalc_rq_segments(struct 
request_queue *q,
 bool no_sg_merge)
 {
struct bio_vec bv, bvprv = { NULL };
-   int cluster, prev = 0;
unsigned int seg_size, nr_phys_segs;
struct bio *fbio, *bbio;
struct bvec_iter iter;
+   bool prev = false;
 
if (!bio)
return 0;
@@ -313,7 +313,6 @@ static unsigned int __blk_recalc_rq_segments(struct 
request_queue *q,
}
 
fbio = bio;
-   cluster = blk_queue_cluster(q);
seg_size = 0;
nr_phys_segs = 0;
for_each_bio(bio) {
@@ -325,7 +324,7 @@ static unsigned int __blk_recalc_rq_segments(struct 
request_queue *q,
if (no_sg_merge)
goto new_segment;
 
-   if (prev && cluster) {
+   if (prev) {
if (seg_size + bv.bv_len
> queue_max_segment_size(q))
goto new_segment;
@@ -343,7 +342,7 @@ static unsigned int __blk_recalc_rq_segments(struct 
request_queue *q,
 
nr_phys_segs++;
bvprv = bv;
-   prev = 1;
+   prev = true;
seg_size = bv.bv_len;
}
bbio = bio;
@@ -396,9 +395,6 @@ static int blk_phys_contig_segment(struct request_queue *q, 
struct bio *bio,
 {
struct bio_vec end_bv = { NULL }, nxt_bv;
 
-   if (!blk_queue_cluster(q))
-   return 0;
-
if (bio->bi_seg_back_size + nxt->bi_seg_front_size >
queue_max_segment_size(q))
return 0;
@@ -415,12 +411,12 @@ static int blk_phys_contig_segment(struct request_queue 
*q, struct bio *bio,
 static inline void
 __blk_segment_map_sg(struct request_queue *q, struct bio_vec *bvec,
 struct scatterlist *sglist, struct bio_vec *bvprv,
-struct scatterlist **sg, int *nsegs, int *cluster)
+struct scatterlist **sg, int *nsegs)
 {
 
int nbytes = bvec->bv_len;
 
-   if (*sg && *cluster) {
+   if (*sg) {
if ((*sg)->length + nbytes > queue_max_segment_size(q))
goto new_segment;
if (!biovec_phys_mergeable(q, bvprv, bvec))
@@ -466,12 +462,12 @@ static int __blk_bios_map_sg(struct request_queue *q, 
struct bio *bio,
 {
struct bio_vec bvec, bvprv = { NULL };
struct bvec_iter iter;
-   int cluster = blk_queue_cluster(q), nsegs = 0;
+   int nsegs = 0;
 
for_each_bio(bio)
bio_for_each_segment(bvec, bio, iter)
__blk_segment_map_sg(q, , sglist, , sg,
-, );
+);
 
return nsegs;
 }
diff --git a/block/blk-settings.c b/block/blk-settings.c
index 3abe831e92c8..3e7038e475ee 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -56,7 +56,6 @@ void blk_set_default_limits(struct queue_limits *lim)
lim->alignment_offset = 0;
lim->io_opt = 0;
lim->misaligned = 0;
-   lim->cluster = 1;
lim->zoned = BLK_ZONED_NONE;
 }
 EXPORT_SYMBOL(blk_set_default_limits);
@@ -547,8 +546,6 @@ int blk_stack_limits(struct queue_limits *t, struct 
queue_limits *b,
t->io_min = max(t->io_min, b->io_min);
t->io_opt = lcm_not_zero(t->io_opt, b->io_opt);
 
-   t->cluster &= b->cluster;
-
/* Physical block size a multiple of the logical block size? */
if