Based on Jens code for sg-chaining but over scsi_sgtable implementation
- Previous scsi_{alloc,free}_sgtable() renamed to scsi_{alloc,free}_sgtable_page()
- scsi_{alloc,free}_sgtable() using the above now supports sg-chaining with multiple
sgtable allocations.
- Report arbitrary default of 2048 to block layer.
from Jens:
This is what enables large commands. If we need to allocate an
sgtable that doesn't fit in a single page, allocate several
SCSI_MAX_SG_SEGMENTS sized tables and chain them together.
SCSI defaults to large chained sg tables, if the arch supports it.
Signed-off-by: Boaz Harrosh <bharrosh@xxxxxxxxxxx>
---
drivers/scsi/scsi_lib.c | 89 +++++++++++++++++++++++++++++++++++++++++++++-
1 files changed, 87 insertions(+), 2 deletions(-)
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 262128c..13870b5 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -59,6 +59,12 @@ static inline unsigned scsi_pool_size(int pool)
return scsi_sg_pools[pool].size;
}
+/*
+ * IO limit For archs that have sg chaining. This limit is totally arbitrary,
+ * a setting of 2048 will get you at least 8mb ios.
+ */
+#define SCSI_MAX_SG_CHAIN_SEGMENTS 2048
+
static void scsi_run_queue(struct request_queue *q);
/*
@@ -713,7 +719,7 @@ static unsigned scsi_sgtable_index(unsigned nents)
return -1;
}
-struct scsi_sgtable *scsi_alloc_sgtable(int sg_count, gfp_t gfp_mask)
+static struct scsi_sgtable *scsi_alloc_sgtable_page(int sg_count, gfp_t gfp_mask)
{
unsigned int pool = scsi_sgtable_index(sg_count);
struct scsi_sgtable *sgt;
@@ -727,12 +733,77 @@ struct scsi_sgtable *scsi_alloc_sgtable(int sg_count, gfp_t gfp_mask)
sgt->sg_pool = pool;
return sgt;
}
+
+struct scsi_sgtable *scsi_alloc_sgtable(int sg_count, gfp_t gfp_mask)
+{
+ struct scsi_sgtable *sgt, *prev, *ret;
+
+ if (sg_count <= SCSI_MAX_SG_SEGMENTS)
+ return scsi_alloc_sgtable_page(sg_count, gfp_mask);
+
+ ret = prev = NULL;
+ do {
+ int this;
+
+ if (sg_count > SCSI_MAX_SG_SEGMENTS) {
+ this = SCSI_MAX_SG_SEGMENTS - 1; /* room for chain */
+ } else {
+ this = sg_count;
+ }
+
+ sgt = scsi_alloc_sgtable_page(this, gfp_mask);
+ /*
+ * FIXME: since second and on allocations are done
+ * ~__GFP_WAIT we can fail more easilly, but nothing
+ * prevents us from trying smaller pools and chaining
+ * more arrays. The last patch in the series does just
+ * that.
+ */
+ if (unlikely(!sgt))
+ goto enomem;
+
+ /* first loop through, set return value */
+ if (!ret)
+ ret = sgt;
+
+ /* chain previous sglist, if any */
+ if (prev)
+ sg_chain(prev->sglist, scsi_pool_size(prev->sg_pool),
+ sgt->sglist);
+
+ /*
+ * don't allow subsequent mempool allocs to sleep, it would
+ * violate the mempool principle.
+ */
+ gfp_mask &= ~__GFP_WAIT;
+ gfp_mask |= __GFP_HIGH;
+ sg_count -= this;
+ prev = sgt;
+ } while (sg_count);
+
+ return ret;
+enomem:
+ if (ret)
+ scsi_free_sgtable(ret);
+ return NULL;
+}
EXPORT_SYMBOL(scsi_alloc_sgtable);
-void scsi_free_sgtable(struct scsi_sgtable *sgt)
+static void scsi_free_sgtable_page(struct scsi_sgtable *sgt)
{
mempool_free(sgt, scsi_sg_pools[sgt->sg_pool].pool);
}
+
+static void scsi_free_sgtable(struct scsi_sgtable *sgt)
+{
+ do {
+ struct scatterlist *next, *here_last;
+ here_last = &sgt->sglist[scsi_pool_size(sgt->sg_pool) - 1];
+ next = sg_is_chain(here_last) ? sg_chain_ptr(here_last) : NULL;
+ scsi_free_sgtable_page(sgt);
+ sgt = next ? ((struct scsi_sgtable*)next) - 1 : NULL;
+ } while(sgt);
+}
EXPORT_SYMBOL(scsi_free_sgtable);
/*
@@ -1550,8 +1621,22 @@ struct request_queue *__scsi_alloc_queue(struct Scsi_Host *shost,
if (!q)
return NULL;
+ /*
+ * this limit is imposed by hardware restrictions
+ */
blk_queue_max_hw_segments(q, shost->sg_tablesize);
+
+ /*
+ * In the future, sg chaining support will be mandatory and this
+ * ifdef can then go away. Right now we don't have all archs
+ * converted, so better keep it safe.
+ */
+#ifdef ARCH_HAS_SG_CHAIN
+ blk_queue_max_phys_segments(q, SCSI_MAX_SG_CHAIN_SEGMENTS);
+#else
blk_queue_max_phys_segments(q, SCSI_MAX_SG_SEGMENTS);
+#endif
+
blk_queue_max_sectors(q, shost->max_sectors);
blk_queue_bounce_limit(q, scsi_calculate_bounce_limit(shost));
blk_queue_segment_boundary(q, shost->dma_boundary);
--
1.5.2.2.249.g45fd
-
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