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>
diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index 3a8e8e8..b4415fc 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -165,6 +165,7 @@
* __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 @@
*
**/
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 @@
}
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 @@
**/
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 @@
*
**/
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 @@
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 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;
}