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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 <hch@lst.de> Cc: Bart Van Assche <bvanassche@acm.org> Cc: Ewan D. Milne <emilne@redhat.com> Cc: Hannes Reinecke <hare@suse.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Ming Lei <ming.lei@redhat.com> Reviewed-by: Bart Van Assche <bvanassche@acm.org> Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
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4635873c56
commit
92524fa123
1 changed files with 11 additions and 3 deletions
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@ -39,6 +39,12 @@
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#include "scsi_priv.h"
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#include "scsi_logging.h"
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/*
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* Size of integrity metadata is usually small, 1 inline sg should
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* cover normal cases.
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*/
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#define SCSI_INLINE_PROT_SG_CNT 1
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static struct kmem_cache *scsi_sdb_cache;
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static struct kmem_cache *scsi_sense_cache;
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static struct kmem_cache *scsi_sense_isadma_cache;
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@ -543,7 +549,8 @@ static void scsi_mq_free_sgtables(struct scsi_cmnd *cmd)
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if (cmd->sdb.table.nents)
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sg_free_table_chained(&cmd->sdb.table, SG_CHUNK_SIZE);
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if (scsi_prot_sg_count(cmd))
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sg_free_table_chained(&cmd->prot_sdb->table, SG_CHUNK_SIZE);
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sg_free_table_chained(&cmd->prot_sdb->table,
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SCSI_INLINE_PROT_SG_CNT);
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}
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static void scsi_mq_uninit_cmd(struct scsi_cmnd *cmd)
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@ -1032,7 +1039,7 @@ blk_status_t scsi_init_io(struct scsi_cmnd *cmd)
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if (sg_alloc_table_chained(&prot_sdb->table, ivecs,
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prot_sdb->table.sgl,
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SG_CHUNK_SIZE)) {
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SCSI_INLINE_PROT_SG_CNT)) {
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ret = BLK_STS_RESOURCE;
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goto out_free_sgtables;
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}
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@ -1824,7 +1831,8 @@ int scsi_mq_setup_tags(struct Scsi_Host *shost)
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sgl_size = scsi_mq_sgl_size(shost);
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cmd_size = sizeof(struct scsi_cmnd) + shost->hostt->cmd_size + sgl_size;
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if (scsi_host_get_prot(shost))
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cmd_size += sizeof(struct scsi_data_buffer) + sgl_size;
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cmd_size += sizeof(struct scsi_data_buffer) +
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sizeof(struct scatterlist) * SCSI_INLINE_PROT_SG_CNT;
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memset(&shost->tag_set, 0, sizeof(shost->tag_set));
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shost->tag_set.ops = &scsi_mq_ops;
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