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vhost-scsi: Allocate iov_iter used for unaligned copies when needed

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It's extremely rare that we get unaligned requests that need to drop
down to the data copy code path. However, the iov_iter is almost 5% of
the mem used for the vhost_scsi_cmd. This patch has us allocate the
iov_iter only when needed since it's not a perf path that uses the
struct. This along with the patches that removed the duplicated fields on
the vhost_scsd_cmd allow us to reduce mem use by 1 MB in mid size setups
where we have 16 virtqueues and are doing 1024 cmds per queue.

Signed-off-by: Mike Christie <michael.christie@oracle.com>
Message-Id: <20241203191705.19431-8-michael.christie@oracle.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Mike Christie 2024-12-03 13:15:14 -06:00 committed by Michael S. Tsirkin
parent ddc5b5f68e
commit fd47976581
1 changed files with 17 additions and 9 deletions
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26
drivers/vhost/scsi.c
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@ -112,8 +112,8 @@ struct vhost_scsi_cmd {
u32 tvc_sgl_count;
u32 tvc_prot_sgl_count;
u32 copied_iov:1;
const void *saved_iter_addr;
struct iov_iter saved_iter;
const void *read_iov;
struct iov_iter *read_iter;
struct scatterlist *sgl;
struct sg_table table;
struct scatterlist *prot_sgl;
@ -378,7 +378,8 @@ static void vhost_scsi_release_cmd_res(struct se_cmd *se_cmd)
else
put_page(page);
}
kfree(tv_cmd->saved_iter_addr);
kfree(tv_cmd->read_iter);
kfree(tv_cmd->read_iov);
sg_free_table_chained(&tv_cmd->table, vs->inline_sg_cnt);
}
if (tv_cmd->tvc_prot_sgl_count) {
@ -576,7 +577,7 @@ static void vhost_scsi_evt_work(struct vhost_work *work)
static int vhost_scsi_copy_sgl_to_iov(struct vhost_scsi_cmd *cmd)
{
struct iov_iter *iter = &cmd->saved_iter;
struct iov_iter *iter = cmd->read_iter;
struct scatterlist *sg;
struct page *page;
size_t len;
@ -624,7 +625,7 @@ static void vhost_scsi_complete_cmd_work(struct vhost_work *work)
cmd, se_cmd->residual_count, se_cmd->scsi_status);
memset(&v_rsp, 0, sizeof(v_rsp));
if (cmd->saved_iter_addr && vhost_scsi_copy_sgl_to_iov(cmd)) {
if (cmd->read_iter && vhost_scsi_copy_sgl_to_iov(cmd)) {
v_rsp.response = VIRTIO_SCSI_S_BAD_TARGET;
} else {
v_rsp.resid = cpu_to_vhost32(cmd->tvc_vq,
@ -808,10 +809,15 @@ vhost_scsi_copy_iov_to_sgl(struct vhost_scsi_cmd *cmd, struct iov_iter *iter,
int i, ret;
if (data_dir == DMA_FROM_DEVICE) {
cmd->saved_iter_addr = dup_iter(&cmd->saved_iter, iter,
GFP_KERNEL);
if (!cmd->saved_iter_addr)
cmd->read_iter = kzalloc(sizeof(*cmd->read_iter), GFP_KERNEL);
if (!cmd->read_iter)
return -ENOMEM;
cmd->read_iov = dup_iter(cmd->read_iter, iter, GFP_KERNEL);
if (!cmd->read_iov) {
ret = -ENOMEM;
goto free_iter;
}
}
for_each_sgtable_sg(sg_table, sg, i) {
@ -845,7 +851,9 @@ vhost_scsi_copy_iov_to_sgl(struct vhost_scsi_cmd *cmd, struct iov_iter *iter,
if (page)
__free_page(page);
}
kfree(cmd->saved_iter_addr);
kfree(cmd->read_iov);
free_iter:
kfree(cmd->read_iter);
return ret;
}