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scatterlist: allow chaining to preallocated chunks 

Blk-mq drivers usually preallocate their S/G list as part of the request,
but if we want to support the very large S/G lists currently supported by
the SCSI code that would tie up a lot of memory in the preallocated request
pool.  Add support to the scatterlist code so that it can initialize a
S/G list that uses a preallocated first chunks and dynamically allocated
additional chunks.  That way the scsi-mq code can preallocate a first
page worth of S/G entries as part of the request, and dynamically extend
the S/G list when needed.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Webb Scales <webbnh@hp.com>
Acked-by: Jens Axboe <axboe@kernel.dk>
Tested-by: Bart Van Assche <bvanassche@acm.org>
Tested-by: Robert Elliott <elliott@hp.com>
hifive-unleashed-5.1
Christoph Hellwig 2014-04-15 14:38:31 +02:00
parent f6d47e74fc
commit c53c6d6a68
3 changed files with 27 additions and 20 deletions
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16
drivers/scsi/scsi_lib.c
View File

@ -564,6 +564,11 @@ static struct scatterlist *scsi_sg_alloc(unsigned int nents, gfp_t gfp_mask)
return mempool_alloc(sgp->pool, gfp_mask);
}
static void scsi_free_sgtable(struct scsi_data_buffer *sdb)
{
__sg_free_table(&sdb->table, SCSI_MAX_SG_SEGMENTS, false, scsi_sg_free);
}
static int scsi_alloc_sgtable(struct scsi_data_buffer *sdb, int nents,
gfp_t gfp_mask)
{
@ -572,19 +577,12 @@ static int scsi_alloc_sgtable(struct scsi_data_buffer *sdb, int nents,
BUG_ON(!nents);
ret = __sg_alloc_table(&sdb->table, nents, SCSI_MAX_SG_SEGMENTS,
gfp_mask, scsi_sg_alloc);
NULL, gfp_mask, scsi_sg_alloc);
if (unlikely(ret))
__sg_free_table(&sdb->table, SCSI_MAX_SG_SEGMENTS,
scsi_sg_free);
scsi_free_sgtable(sdb);
return ret;
}
static void scsi_free_sgtable(struct scsi_data_buffer *sdb)
{
__sg_free_table(&sdb->table, SCSI_MAX_SG_SEGMENTS, scsi_sg_free);
}
/*
* Function: scsi_release_buffers()
*

6
include/linux/scatterlist.h
View File

@ -229,10 +229,10 @@ void sg_init_one(struct scatterlist *, const void *, unsigned int);
typedef struct scatterlist *(sg_alloc_fn)(unsigned int, gfp_t);
typedef void (sg_free_fn)(struct scatterlist *, unsigned int);
void __sg_free_table(struct sg_table *, unsigned int, sg_free_fn *);
void __sg_free_table(struct sg_table *, unsigned int, bool, sg_free_fn *);
void sg_free_table(struct sg_table *);
int __sg_alloc_table(struct sg_table *, unsigned int, unsigned int, gfp_t,
sg_alloc_fn *);
int __sg_alloc_table(struct sg_table *, unsigned int, unsigned int,
struct scatterlist *, gfp_t, sg_alloc_fn *);
int sg_alloc_table(struct sg_table *, unsigned int, gfp_t);
int sg_alloc_table_from_pages(struct sg_table *sgt,
struct page **pages, unsigned int n_pages,

25
lib/scatterlist.c
View File

@ -165,6 +165,7 @@ static void sg_kfree(struct scatterlist *sg, unsigned int nents)
* __sg_free_table - Free a previously mapped sg table
* @table: The sg table header to use
* @max_ents: The maximum number of entries per single scatterlist
* @skip_first_chunk: don't free the (preallocated) first scatterlist chunk
* @free_fn: Free function
*
* Description:
@ -174,7 +175,7 @@ static void sg_kfree(struct scatterlist *sg, unsigned int nents)
*
**/
void __sg_free_table(struct sg_table *table, unsigned int max_ents,
sg_free_fn *free_fn)
bool skip_first_chunk, sg_free_fn *free_fn)
{
struct scatterlist *sgl, *next;
@ -202,7 +203,10 @@ void __sg_free_table(struct sg_table *table, unsigned int max_ents,
}
table->orig_nents -= sg_size;
free_fn(sgl, alloc_size);
if (!skip_first_chunk) {
free_fn(sgl, alloc_size);
skip_first_chunk = false;
}
sgl = next;
}
@ -217,7 +221,7 @@ EXPORT_SYMBOL(__sg_free_table);
**/
void sg_free_table(struct sg_table *table)
{
__sg_free_table(table, SG_MAX_SINGLE_ALLOC, sg_kfree);
__sg_free_table(table, SG_MAX_SINGLE_ALLOC, false, sg_kfree);
}
EXPORT_SYMBOL(sg_free_table);
@ -241,8 +245,8 @@ EXPORT_SYMBOL(sg_free_table);
*
**/
int __sg_alloc_table(struct sg_table *table, unsigned int nents,
unsigned int max_ents, gfp_t gfp_mask,
sg_alloc_fn *alloc_fn)
unsigned int max_ents, struct scatterlist *first_chunk,
gfp_t gfp_mask, sg_alloc_fn *alloc_fn)
{
struct scatterlist *sg, *prv;
unsigned int left;
@ -269,7 +273,12 @@ int __sg_alloc_table(struct sg_table *table, unsigned int nents,
left -= sg_size;
sg = alloc_fn(alloc_size, gfp_mask);
if (first_chunk) {
sg = first_chunk;
first_chunk = NULL;
} else {
sg = alloc_fn(alloc_size, gfp_mask);
}
if (unlikely(!sg)) {
/*
* Adjust entry count to reflect that the last
@ -324,9 +333,9 @@ int sg_alloc_table(struct sg_table *table, unsigned int nents, gfp_t gfp_mask)
int ret;
ret = __sg_alloc_table(table, nents, SG_MAX_SINGLE_ALLOC,
gfp_mask, sg_kmalloc);
NULL, gfp_mask, sg_kmalloc);
if (unlikely(ret))
__sg_free_table(table, SG_MAX_SINGLE_ALLOC, sg_kfree);
__sg_free_table(table, SG_MAX_SINGLE_ALLOC, false, sg_kfree);
return ret;
}