Messages in this thread Patch in this message | | | From | "Fabio M. De Francesco" <> | Subject | [PATCH] nvmet-tcp: Don't kmap() pages which can't come from HIGHMEM | Date | Wed, 17 Aug 2022 19:04:27 +0200 |
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kmap() is being deprecated in favor of kmap_local_page().[1]
There are two main problems with kmap(): (1) It comes with an overhead as mapping space is restricted and protected by a global lock for synchronization and (2) it also requires global TLB invalidation when the kmap’s pool wraps and it might block when the mapping space is fully utilized until a slot becomes available.
The pages which will be mapped are allocated in nvmet_tcp_map_data(), using the GFP_KERNEL flag. This assures that they cannot come from HIGHMEM. This imply that a straight page_address() can replace the kmap() of sg_page(sg) in nvmet_tcp_map_pdu_iovec(). As a side effect, we might also delete the field "nr_mapped" from struct "nvmet_tcp_cmd" because, after removing the kmap() calls, there would be no longer any need of it.
Therefore, replace the kmap() of sg_page(sg) with a page_address() and delete the "nr_mapped" field from "nvmet_tcp_cmd".
[1] "[PATCH] checkpatch: Add kmap and kmap_atomic to the deprecated list" https://lore.kernel.org/all/20220813220034.806698-1-ira.weiny@intel.com/
Cc: Chaitanya Kulkarni <chaitanyak@nvidia.com> Cc: Keith Busch <kbusch@kernel.org> Cc: Sagi Grimberg <sagi@grimberg.me> Suggested-by: Ira Weiny <ira.weiny@intel.com> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com> ---
Thanks so much to Chaitanya, Keith, Sagi, for the answers and the comments on the RFC which gave birth to this patch. The RFC is at: https://lore.kernel.org/all/20220816091808.23236-1-fmdefrancesco@gmail.com/
drivers/nvme/target/tcp.c | 26 ++------------------------ 1 file changed, 2 insertions(+), 24 deletions(-)
diff --git a/drivers/nvme/target/tcp.c b/drivers/nvme/target/tcp.c index dc3b4dc8fe08..6ed44531de55 100644 --- a/drivers/nvme/target/tcp.c +++ b/drivers/nvme/target/tcp.c @@ -77,7 +77,6 @@ struct nvmet_tcp_cmd { u32 pdu_len; u32 pdu_recv; int sg_idx; - int nr_mapped; struct msghdr recv_msg; struct kvec *iov; u32 flags; @@ -167,7 +166,6 @@ static const struct nvmet_fabrics_ops nvmet_tcp_ops; static void nvmet_tcp_free_cmd(struct nvmet_tcp_cmd *c); static void nvmet_tcp_finish_cmd(struct nvmet_tcp_cmd *cmd); static void nvmet_tcp_free_cmd_buffers(struct nvmet_tcp_cmd *cmd); -static void nvmet_tcp_unmap_pdu_iovec(struct nvmet_tcp_cmd *cmd); static inline u16 nvmet_tcp_cmd_tag(struct nvmet_tcp_queue *queue, struct nvmet_tcp_cmd *cmd) @@ -301,27 +299,12 @@ static int nvmet_tcp_check_ddgst(struct nvmet_tcp_queue *queue, void *pdu) static void nvmet_tcp_free_cmd_buffers(struct nvmet_tcp_cmd *cmd) { - WARN_ON(unlikely(cmd->nr_mapped > 0)); - kfree(cmd->iov); sgl_free(cmd->req.sg); cmd->iov = NULL; cmd->req.sg = NULL; } -static void nvmet_tcp_unmap_pdu_iovec(struct nvmet_tcp_cmd *cmd) -{ - struct scatterlist *sg; - int i; - - sg = &cmd->req.sg[cmd->sg_idx]; - - for (i = 0; i < cmd->nr_mapped; i++) - kunmap(sg_page(&sg[i])); - - cmd->nr_mapped = 0; -} - static void nvmet_tcp_map_pdu_iovec(struct nvmet_tcp_cmd *cmd) { struct kvec *iov = cmd->iov; @@ -329,7 +312,6 @@ static void nvmet_tcp_map_pdu_iovec(struct nvmet_tcp_cmd *cmd) u32 length, offset, sg_offset; length = cmd->pdu_len; - cmd->nr_mapped = DIV_ROUND_UP(length, PAGE_SIZE); offset = cmd->rbytes_done; cmd->sg_idx = offset / PAGE_SIZE; sg_offset = offset % PAGE_SIZE; @@ -338,7 +320,7 @@ static void nvmet_tcp_map_pdu_iovec(struct nvmet_tcp_cmd *cmd) while (length) { u32 iov_len = min_t(u32, length, sg->length - sg_offset); - iov->iov_base = kmap(sg_page(sg)) + sg->offset + sg_offset; + iov->iov_base = page_address(sg_page(sg)) + sg->offset + sg_offset; iov->iov_len = iov_len; length -= iov_len; @@ -347,8 +329,7 @@ static void nvmet_tcp_map_pdu_iovec(struct nvmet_tcp_cmd *cmd) sg_offset = 0; } - iov_iter_kvec(&cmd->recv_msg.msg_iter, READ, cmd->iov, - cmd->nr_mapped, cmd->pdu_len); + iov_iter_kvec(&cmd->recv_msg.msg_iter, READ, cmd->iov, 0, cmd->pdu_len); } static void nvmet_tcp_fatal_error(struct nvmet_tcp_queue *queue) @@ -1141,7 +1122,6 @@ static int nvmet_tcp_try_recv_data(struct nvmet_tcp_queue *queue) cmd->rbytes_done += ret; } - nvmet_tcp_unmap_pdu_iovec(cmd); if (queue->data_digest) { nvmet_tcp_prep_recv_ddgst(cmd); return 0; @@ -1411,7 +1391,6 @@ static void nvmet_tcp_restore_socket_callbacks(struct nvmet_tcp_queue *queue) static void nvmet_tcp_finish_cmd(struct nvmet_tcp_cmd *cmd) { nvmet_req_uninit(&cmd->req); - nvmet_tcp_unmap_pdu_iovec(cmd); nvmet_tcp_free_cmd_buffers(cmd); } @@ -1424,7 +1403,6 @@ static void nvmet_tcp_uninit_data_in_cmds(struct nvmet_tcp_queue *queue) if (nvmet_tcp_need_data_in(cmd)) nvmet_req_uninit(&cmd->req); - nvmet_tcp_unmap_pdu_iovec(cmd); nvmet_tcp_free_cmd_buffers(cmd); } -- 2.37.1
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