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Date: Mon, 16 Jul 2007 11:47:30 +0200
From: Jens Axboe <jens.axboe@...cle.com>
To: linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org
Cc: Jens Axboe <jens.axboe@...cle.com>, fujita.tomonori@....ntt.co.jp,
James.Bottomley@...elEye.com
Subject: [PATCH 16/33] SCSI: support for allocating large scatterlists
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.
Cc: fujita.tomonori@....ntt.co.jp
Cc: James.Bottomley@...elEye.com
Signed-off-by: Jens Axboe <jens.axboe@...cle.com>
---
drivers/scsi/scsi_lib.c | 208 ++++++++++++++++++++++++++++++++++++----------
include/scsi/scsi.h | 7 --
include/scsi/scsi_cmnd.h | 1 +
3 files changed, 163 insertions(+), 53 deletions(-)
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 0b4610c..60bb557 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -36,33 +36,20 @@
struct scsi_host_sg_pool {
size_t size;
- char *name;
+ char *name;
struct kmem_cache *slab;
mempool_t *pool;
};
-#if (SCSI_MAX_PHYS_SEGMENTS < 32)
-#error SCSI_MAX_PHYS_SEGMENTS is too small
-#endif
-
-#define SP(x) { x, "sgpool-" #x }
+#define SP(x) { x, "sgpool-" #x }
static struct scsi_host_sg_pool scsi_sg_pools[] = {
SP(8),
SP(16),
SP(32),
-#if (SCSI_MAX_PHYS_SEGMENTS > 32)
SP(64),
-#if (SCSI_MAX_PHYS_SEGMENTS > 64)
SP(128),
-#if (SCSI_MAX_PHYS_SEGMENTS > 128)
SP(256),
-#if (SCSI_MAX_PHYS_SEGMENTS > 256)
-#error SCSI_MAX_PHYS_SEGMENTS is too large
-#endif
-#endif
-#endif
-#endif
-};
+};
#undef SP
static void scsi_run_queue(struct request_queue *q);
@@ -703,45 +690,126 @@ static struct scsi_cmnd *scsi_end_request(struct scsi_cmnd *cmd, int uptodate,
return NULL;
}
-struct scatterlist *scsi_alloc_sgtable(struct scsi_cmnd *cmd, gfp_t gfp_mask)
-{
- struct scsi_host_sg_pool *sgp;
- struct scatterlist *sgl;
+/*
+ * The maximum number of SG segments that we will put inside a scatterlist
+ * (unless chaining is used). Should ideally fit inside a single page, to
+ * avoid a higher order allocation.
+ */
+#define SCSI_MAX_SG_SEGMENTS 128
- BUG_ON(!cmd->use_sg);
+/*
+ * Like SCSI_MAX_SG_SEGMENTS, but 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
- switch (cmd->use_sg) {
+static inline unsigned int scsi_sgtable_index(unsigned short nents)
+{
+ unsigned int index;
+
+ switch (nents) {
case 1 ... 8:
- cmd->sglist_len = 0;
+ index = 0;
break;
case 9 ... 16:
- cmd->sglist_len = 1;
+ index = 1;
break;
case 17 ... 32:
- cmd->sglist_len = 2;
+ index = 2;
break;
-#if (SCSI_MAX_PHYS_SEGMENTS > 32)
case 33 ... 64:
- cmd->sglist_len = 3;
+ index = 3;
break;
-#if (SCSI_MAX_PHYS_SEGMENTS > 64)
- case 65 ... 128:
- cmd->sglist_len = 4;
+ case 65 ... SCSI_MAX_SG_SEGMENTS:
+ index = 4;
break;
-#if (SCSI_MAX_PHYS_SEGMENTS > 128)
- case 129 ... 256:
- cmd->sglist_len = 5;
- break;
-#endif
-#endif
-#endif
default:
- return NULL;
+ printk(KERN_ERR "scsi: bad segment count=%d\n", nents);
+ BUG();
}
- sgp = scsi_sg_pools + cmd->sglist_len;
- sgl = mempool_alloc(sgp->pool, gfp_mask);
- return sgl;
+ return index;
+}
+
+struct scatterlist *scsi_alloc_sgtable(struct scsi_cmnd *cmd, gfp_t gfp_mask)
+{
+ struct scsi_host_sg_pool *sgp;
+ struct scatterlist *sgl, *prev, *ret;
+ unsigned int index;
+ int this, left;
+
+ BUG_ON(!cmd->use_sg);
+
+ left = cmd->use_sg;
+ ret = prev = NULL;
+ do {
+ this = left;
+ if (this > SCSI_MAX_SG_SEGMENTS) {
+ this = SCSI_MAX_SG_SEGMENTS - 1;
+ index = SG_MEMPOOL_NR - 1;
+ } else
+ index = scsi_sgtable_index(this);
+
+ left -= this;
+
+ sgp = scsi_sg_pools + index;
+
+ sgl = mempool_alloc(sgp->pool, gfp_mask);
+ if (unlikely(!sgl))
+ goto enomem;
+
+ memset(sgl, 0, sizeof(*sgl) * sgp->size);
+
+ /*
+ * first loop through, set initial index and return value
+ */
+ if (!ret) {
+ cmd->sglist_len = index;
+ ret = sgl;
+ }
+
+ /*
+ * chain previous sglist, if any. we know the previous
+ * sglist must be the biggest one, or we would not have
+ * ended up doing another loop.
+ */
+ if (prev)
+ sg_chain(prev, SCSI_MAX_SG_SEGMENTS, sgl);
+
+ /*
+ * don't allow subsequent mempool allocs to sleep, it would
+ * violate the mempool principle.
+ */
+ gfp_mask &= ~__GFP_WAIT;
+ gfp_mask |= __GFP_HIGH;
+ prev = sgl;
+ } while (left);
+
+ /*
+ * ->use_sg may get modified after dma mapping has potentially
+ * shrunk the number of segments, so keep a copy of it for free.
+ */
+ cmd->__use_sg = cmd->use_sg;
+ return ret;
+enomem:
+ if (ret) {
+ /*
+ * Free entries chained off ret. Since we were trying to
+ * allocate another sglist, we know that all entries are of
+ * the max size.
+ */
+ sgp = scsi_sg_pools + SG_MEMPOOL_NR - 1;
+ prev = ret;
+ ret = &ret[SCSI_MAX_SG_SEGMENTS - 1];
+
+ while ((sgl = sg_chain_ptr(ret)) != NULL) {
+ ret = &sgl[SCSI_MAX_SG_SEGMENTS - 1];
+ mempool_free(sgl, sgp->pool);
+ }
+
+ mempool_free(prev, sgp->pool);
+ }
+ return NULL;
}
EXPORT_SYMBOL(scsi_alloc_sgtable);
@@ -753,6 +821,42 @@ void scsi_free_sgtable(struct scsi_cmnd *cmd)
BUG_ON(cmd->sglist_len >= SG_MEMPOOL_NR);
+ /*
+ * if this is the biggest size sglist, check if we have
+ * chained parts we need to free
+ */
+ if (cmd->__use_sg > SCSI_MAX_SG_SEGMENTS) {
+ unsigned short this, left;
+ struct scatterlist *next;
+ unsigned int index;
+
+ left = cmd->__use_sg - (SCSI_MAX_SG_SEGMENTS - 1);
+ next = sg_chain_ptr(&sgl[SCSI_MAX_SG_SEGMENTS - 1]);
+ while (left && next) {
+ sgl = next;
+ this = left;
+ if (this > SCSI_MAX_SG_SEGMENTS) {
+ this = SCSI_MAX_SG_SEGMENTS - 1;
+ index = SG_MEMPOOL_NR - 1;
+ } else
+ index = scsi_sgtable_index(this);
+
+ left -= this;
+
+ sgp = scsi_sg_pools + index;
+
+ if (left)
+ next = sg_chain_ptr(&sgl[sgp->size - 1]);
+
+ mempool_free(sgl, sgp->pool);
+ }
+
+ /*
+ * Restore original, will be freed below
+ */
+ sgl = cmd->request_buffer;
+ }
+
sgp = scsi_sg_pools + cmd->sglist_len;
mempool_free(sgl, sgp->pool);
}
@@ -994,7 +1098,6 @@ EXPORT_SYMBOL(scsi_io_completion);
static int scsi_init_io(struct scsi_cmnd *cmd)
{
struct request *req = cmd->request;
- struct scatterlist *sgpnt;
int count;
/*
@@ -1007,14 +1110,13 @@ static int scsi_init_io(struct scsi_cmnd *cmd)
/*
* If sg table allocation fails, requeue request later.
*/
- sgpnt = scsi_alloc_sgtable(cmd, GFP_ATOMIC);
- if (unlikely(!sgpnt)) {
+ cmd->request_buffer = scsi_alloc_sgtable(cmd, GFP_ATOMIC);
+ if (unlikely(!cmd->request_buffer)) {
scsi_unprep_request(req);
return BLKPREP_DEFER;
}
req->buffer = NULL;
- cmd->request_buffer = (char *) sgpnt;
if (blk_pc_request(req))
cmd->request_bufflen = req->data_len;
else
@@ -1578,8 +1680,22 @@ 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);
- blk_queue_max_phys_segments(q, SCSI_MAX_PHYS_SEGMENTS);
+
+ /*
+ * 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);
diff --git a/include/scsi/scsi.h b/include/scsi/scsi.h
index 9f8f80a..702fcfe 100644
--- a/include/scsi/scsi.h
+++ b/include/scsi/scsi.h
@@ -11,13 +11,6 @@
#include <linux/types.h>
/*
- * The maximum sg list length SCSI can cope with
- * (currently must be a power of 2 between 32 and 256)
- */
-#define SCSI_MAX_PHYS_SEGMENTS MAX_PHYS_SEGMENTS
-
-
-/*
* SCSI command lengths
*/
diff --git a/include/scsi/scsi_cmnd.h b/include/scsi/scsi_cmnd.h
index 760d4a5..937b3c4 100644
--- a/include/scsi/scsi_cmnd.h
+++ b/include/scsi/scsi_cmnd.h
@@ -72,6 +72,7 @@ struct scsi_cmnd {
/* These elements define the operation we ultimately want to perform */
unsigned short use_sg; /* Number of pieces of scatter-gather */
unsigned short sglist_len; /* size of malloc'd scatter-gather list */
+ unsigned short __use_sg;
unsigned underflow; /* Return error if less than
this amount is transferred */
--
1.5.3.rc0.90.gbaa79
-
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