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SubjectRe: [PATCH 12/14] scatterlist: allow chaining to preallocated chunks
On 06/25/2014 06:51 PM, Christoph Hellwig wrote:
> 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 extent
> the S/G list when needed.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> drivers/scsi/scsi_lib.c | 16 +++++++---------
> include/linux/scatterlist.h | 6 +++---
> lib/scatterlist.c | 24 ++++++++++++++++--------
> 3 files changed, 26 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index 58534fd..900b1c0 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -567,6 +567,11 @@ 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)
> {
> @@ -575,19 +580,12 @@ 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()
> *
> diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
> index a964f72..f4ec8bb 100644
> --- a/include/linux/scatterlist.h
> +++ b/include/linux/scatterlist.h
> @@ -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,
> diff --git a/lib/scatterlist.c b/lib/scatterlist.c
> index 3a8e8e8..48c15d2 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 +203,9 @@ 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 +220,7 @@ 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 +244,8 @@ 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 +272,12 @@ 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 +332,9 @@ 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;
> }
>
Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
--
Dr. Hannes Reinecke zSeries & Storage
hare@suse.de +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
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