From 92524fa12312d1f082a473e14c590c48b4ef3fe5 Mon Sep 17 00:00:00 2001 From: Ming Lei Date: Sun, 28 Apr 2019 15:39:31 +0800 Subject: scsi: core: avoid preallocating big SGL for protection information scsi_mq_setup_tags() currently preallocates a big buffer for protection SGL entries. scsi_mq_sgl_size() is used to determine the size for both data and protection information scatterlists but the protection buffer is usually much smaller. For example, one 512-byte sector needs 8 bytes of protection information. Given that the maximum number of sectors for one request is 2560 (BLK_DEF_MAX_SECTORS) sectors, the max protection information buffer size is just 20K. The protection information segment count generally matches the number of bios in the request. As a result, the typical actual number of segments won't be very big. And should the need arise, allocating a bigger SGL from slab is fast enough. Pre-allocate only one SGL entry for protection information and switch to runtime allocation in case that the protection information segment number is bigger than 1. This reduces memory tied up by static command allocations. For example, 500+ MB is saved on single lpfc HBA. [mkp: attempted to clarify commit desc] Cc: Christoph Hellwig Cc: Bart Van Assche Cc: Ewan D. Milne Cc: Hannes Reinecke Reviewed-by: Christoph Hellwig Signed-off-by: Ming Lei Reviewed-by: Bart Van Assche Signed-off-by: Martin K. Petersen --- drivers/scsi/scsi_lib.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c index acc0f7080f18..c115458c835e 100644 --- a/drivers/scsi/scsi_lib.c +++ b/drivers/scsi/scsi_lib.c @@ -39,6 +39,12 @@ #include "scsi_priv.h" #include "scsi_logging.h" +/* + * Size of integrity metadata is usually small, 1 inline sg should + * cover normal cases. + */ +#define SCSI_INLINE_PROT_SG_CNT 1 + static struct kmem_cache *scsi_sdb_cache; static struct kmem_cache *scsi_sense_cache; static struct kmem_cache *scsi_sense_isadma_cache; @@ -543,7 +549,8 @@ static void scsi_mq_free_sgtables(struct scsi_cmnd *cmd) if (cmd->sdb.table.nents) sg_free_table_chained(&cmd->sdb.table, SG_CHUNK_SIZE); if (scsi_prot_sg_count(cmd)) - sg_free_table_chained(&cmd->prot_sdb->table, SG_CHUNK_SIZE); + sg_free_table_chained(&cmd->prot_sdb->table, + SCSI_INLINE_PROT_SG_CNT); } static void scsi_mq_uninit_cmd(struct scsi_cmnd *cmd) @@ -1032,7 +1039,7 @@ blk_status_t scsi_init_io(struct scsi_cmnd *cmd) if (sg_alloc_table_chained(&prot_sdb->table, ivecs, prot_sdb->table.sgl, - SG_CHUNK_SIZE)) { + SCSI_INLINE_PROT_SG_CNT)) { ret = BLK_STS_RESOURCE; goto out_free_sgtables; } @@ -1824,7 +1831,8 @@ int scsi_mq_setup_tags(struct Scsi_Host *shost) sgl_size = scsi_mq_sgl_size(shost); cmd_size = sizeof(struct scsi_cmnd) + shost->hostt->cmd_size + sgl_size; if (scsi_host_get_prot(shost)) - cmd_size += sizeof(struct scsi_data_buffer) + sgl_size; + cmd_size += sizeof(struct scsi_data_buffer) + + sizeof(struct scatterlist) * SCSI_INLINE_PROT_SG_CNT; memset(&shost->tag_set, 0, sizeof(shost->tag_set)); shost->tag_set.ops = &scsi_mq_ops; -- cgit v1.2.3