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authorChristoph Hellwig <hch@lst.de>2014-04-15 14:38:31 +0200
committerChristoph Hellwig <hch@lst.de>2014-07-25 17:16:21 -0400
commitc53c6d6a68b13b1dff2892551b56cfdc07887d9e (patch)
tree8bd6ddc1ff0f33e357ad6c230f62fd7b1cf1b28a /lib
parentf6d47e74fcb2814225e429c94355ad1c551daffb (diff)
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>
Diffstat (limited to 'lib')
-rw-r--r--lib/scatterlist.c25
1 files changed, 17 insertions, 8 deletions
diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index 3a8e8e8fb2a5..b4415fceb7e7 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -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;
}