From c53c6d6a68b13b1dff2892551b56cfdc07887d9e Mon Sep 17 00:00:00 2001 From: Christoph Hellwig Date: Tue, 15 Apr 2014 14:38:31 +0200 Subject: 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 Reviewed-by: Martin K. Petersen Reviewed-by: Hannes Reinecke Reviewed-by: Webb Scales Acked-by: Jens Axboe Tested-by: Bart Van Assche Tested-by: Robert Elliott --- lib/scatterlist.c | 25 +++++++++++++++++-------- 1 file changed, 17 insertions(+), 8 deletions(-) (limited to 'lib/scatterlist.c') 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; } -- cgit v1.2.3-59-g8ed1b