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SubjectRe: [Patch v2 10/15] CIFS: SMBD: Support page offset in memory registration
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On 5/30/2018 3:48 PM, Long Li wrote:
> From: Long Li <longli@microsoft.com>
>
> Change code to pass the correct page offset during memory registration for
> RDMA read/write.
>
> Signed-off-by: Long Li <longli@microsoft.com>
> ---
> fs/cifs/smb2pdu.c | 18 ++++++++-----
> fs/cifs/smbdirect.c | 76 +++++++++++++++++++++++++++++++----------------------
> fs/cifs/smbdirect.h | 2 +-
> 3 files changed, 58 insertions(+), 38 deletions(-)
>
> diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
> index f603fbe..fc30774 100644
> --- a/fs/cifs/smb2pdu.c
> +++ b/fs/cifs/smb2pdu.c
> @@ -2623,8 +2623,8 @@ smb2_new_read_req(void **buf, unsigned int *total_len,
>
> rdata->mr = smbd_register_mr(
> server->smbd_conn, rdata->pages,
> - rdata->nr_pages, rdata->tailsz,
> - true, need_invalidate);
> + rdata->nr_pages, rdata->page_offset,
> + rdata->tailsz, true, need_invalidate);
> if (!rdata->mr)
> return -ENOBUFS;
>
> @@ -3013,16 +3013,22 @@ smb2_async_writev(struct cifs_writedata *wdata,
>
> wdata->mr = smbd_register_mr(
> server->smbd_conn, wdata->pages,
> - wdata->nr_pages, wdata->tailsz,
> - false, need_invalidate);
> + wdata->nr_pages, wdata->page_offset,
> + wdata->tailsz, false, need_invalidate);
> if (!wdata->mr) {
> rc = -ENOBUFS;
> goto async_writev_out;
> }
> req->Length = 0;
> req->DataOffset = 0;
> - req->RemainingBytes =
> - cpu_to_le32((wdata->nr_pages-1)*PAGE_SIZE + wdata->tailsz);
> + if (wdata->nr_pages > 1)
> + req->RemainingBytes =
> + cpu_to_le32(
> + (wdata->nr_pages - 1) * wdata->pagesz -
> + wdata->page_offset + wdata->tailsz
> + );
> + else
> + req->RemainingBytes = cpu_to_le32(wdata->tailsz);

Again, I think a helper that computed and returned this size would be
much clearer and compact. And I still am incredulous that a single page
io always has an offset of zero. :-)

> req->Channel = SMB2_CHANNEL_RDMA_V1_INVALIDATE;
> if (need_invalidate)
> req->Channel = SMB2_CHANNEL_RDMA_V1;
> diff --git a/fs/cifs/smbdirect.c b/fs/cifs/smbdirect.c
> index ba53c52..e459c97 100644
> --- a/fs/cifs/smbdirect.c
> +++ b/fs/cifs/smbdirect.c
> @@ -2299,37 +2299,37 @@ static void smbd_mr_recovery_work(struct work_struct *work)
> if (smbdirect_mr->state == MR_INVALIDATED ||
> smbdirect_mr->state == MR_ERROR) {
>
> - if (smbdirect_mr->state == MR_INVALIDATED) {
> + /* recover this MR entry */
> + rc = ib_dereg_mr(smbdirect_mr->mr);
> + if (rc) {
> + log_rdma_mr(ERR,
> + "ib_dereg_mr failed rc=%x\n",
> + rc);
> + smbd_disconnect_rdma_connection(info);
> + continue;
> + }

Ok, we discussed this ib_dereg_mr() call at the plugfest last week.
It's unnecessary - the MR is reusable and does not need to be destroyed
after each use.

> +
> + smbdirect_mr->mr = ib_alloc_mr(
> + info->pd, info->mr_type,
> + info->max_frmr_depth);
> + if (IS_ERR(smbdirect_mr->mr)) {
> + log_rdma_mr(ERR,
> + "ib_alloc_mr failed mr_type=%x "
> + "max_frmr_depth=%x\n",
> + info->mr_type,
> + info->max_frmr_depth);
> + smbd_disconnect_rdma_connection(info);
> + continue;
> + }
> +

Not needed, for the same reason above.

> + if (smbdirect_mr->state == MR_INVALIDATED)
> ib_dma_unmap_sg(
> info->id->device, smbdirect_mr->sgl,
> smbdirect_mr->sgl_count,
> smbdirect_mr->dir);
> - smbdirect_mr->state = MR_READY;

As we observed, the smbdirect_mr is not protected by a lock, therefore
this MR_READY state transition needs a memory barrier in front of it!

> - } else if (smbdirect_mr->state == MR_ERROR) {
> -
> - /* recover this MR entry */
> - rc = ib_dereg_mr(smbdirect_mr->mr);
> - if (rc) {
> - log_rdma_mr(ERR,
> - "ib_dereg_mr failed rc=%x\n",
> - rc);
> - smbd_disconnect_rdma_connection(info);
> - }
Why are you deleting the MR_ERROR handling? It seems this is precisely
the place where the MR needs to be destroyed, to prevent any later RDMA
operations from potentially reaching the original memory.

>
> - smbdirect_mr->mr = ib_alloc_mr(
> - info->pd, info->mr_type,
> - info->max_frmr_depth);
> - if (IS_ERR(smbdirect_mr->mr)) {
> - log_rdma_mr(ERR,
> - "ib_alloc_mr failed mr_type=%x "
> - "max_frmr_depth=%x\n",
> - info->mr_type,
> - info->max_frmr_depth);
> - smbd_disconnect_rdma_connection(info);
> - }
> + smbdirect_mr->state = MR_READY;
>
> - smbdirect_mr->state = MR_READY;
> - }
> /* smbdirect_mr->state is updated by this function
> * and is read and updated by I/O issuing CPUs trying
> * to get a MR, the call to atomic_inc_return
> @@ -2475,7 +2475,7 @@ static struct smbd_mr *get_mr(struct smbd_connection *info)
> */
> struct smbd_mr *smbd_register_mr(
> struct smbd_connection *info, struct page *pages[], int num_pages,
> - int tailsz, bool writing, bool need_invalidate)
> + int offset, int tailsz, bool writing, bool need_invalidate)
> {
> struct smbd_mr *smbdirect_mr;
> int rc, i;
> @@ -2498,17 +2498,31 @@ struct smbd_mr *smbd_register_mr(
> smbdirect_mr->sgl_count = num_pages;
> sg_init_table(smbdirect_mr->sgl, num_pages);
>
> - for (i = 0; i < num_pages - 1; i++)
> - sg_set_page(&smbdirect_mr->sgl[i], pages[i], PAGE_SIZE, 0);
> + log_rdma_mr(INFO, "num_pages=0x%x offset=0x%x tailsz=0x%x\n",
> + num_pages, offset, tailsz);
>
> + if (num_pages == 1) {
> + sg_set_page(&smbdirect_mr->sgl[0], pages[0], tailsz, offset);
> + goto skip_multiple_pages;

A simple "else" would be much preferable to this "goto".

> + }
> +
> + /* We have at least two pages to register */
> + sg_set_page(
> + &smbdirect_mr->sgl[0], pages[0], PAGE_SIZE - offset, offset);
> + i = 1;
> + while (i < num_pages - 1) {
> + sg_set_page(&smbdirect_mr->sgl[i], pages[i], PAGE_SIZE, 0);
> + i++;
> + }
> sg_set_page(&smbdirect_mr->sgl[i], pages[i],
> tailsz ? tailsz : PAGE_SIZE, 0);
>
> +skip_multiple_pages:
> dir = writing ? DMA_FROM_DEVICE : DMA_TO_DEVICE;
> smbdirect_mr->dir = dir;
> rc = ib_dma_map_sg(info->id->device, smbdirect_mr->sgl, num_pages, dir);
> if (!rc) {
> - log_rdma_mr(INFO, "ib_dma_map_sg num_pages=%x dir=%x rc=%x\n",
> + log_rdma_mr(ERR, "ib_dma_map_sg num_pages=%x dir=%x rc=%x\n",
> num_pages, dir, rc);
> goto dma_map_error;
> }
> @@ -2516,8 +2530,8 @@ struct smbd_mr *smbd_register_mr(
> rc = ib_map_mr_sg(smbdirect_mr->mr, smbdirect_mr->sgl, num_pages,
> NULL, PAGE_SIZE);
> if (rc != num_pages) {
> - log_rdma_mr(INFO,
> - "ib_map_mr_sg failed rc = %x num_pages = %x\n",
> + log_rdma_mr(ERR,
> + "ib_map_mr_sg failed rc = %d num_pages = %x\n",
> rc, num_pages);
> goto map_mr_error;
> }
> diff --git a/fs/cifs/smbdirect.h b/fs/cifs/smbdirect.h
> index f9038da..1e419c2 100644
> --- a/fs/cifs/smbdirect.h
> +++ b/fs/cifs/smbdirect.h
> @@ -321,7 +321,7 @@ struct smbd_mr {
> /* Interfaces to register and deregister MR for RDMA read/write */
> struct smbd_mr *smbd_register_mr(
> struct smbd_connection *info, struct page *pages[], int num_pages,
> - int tailsz, bool writing, bool need_invalidate);
> + int offset, int tailsz, bool writing, bool need_invalidate);
> int smbd_deregister_mr(struct smbd_mr *mr);
>
> #else
>

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