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Date: Fri, 21 Sep 2018 15:18:41 -0700
From: Pavel Shilovsky <piastryyy@...il.com>
To: Long Li <longli@...rosoft.com>
Cc: Steve French <sfrench@...ba.org>,
linux-cifs <linux-cifs@...r.kernel.org>,
samba-technical <samba-technical@...ts.samba.org>,
Kernel Mailing List <linux-kernel@...r.kernel.org>,
linux-rdma@...r.kernel.org
Subject: Re: [PATCH V3 (resend) 3/7] CIFS: Add support for direct I/O read
чт, 20 сент. 2018 г. в 14:22, Long Li <longli@...uxonhyperv.com>:
>
> From: Long Li <longli@...rosoft.com>
>
> With direct I/O read, we transfer the data directly from transport layer to
> the user data buffer.
>
> Change in v3: add support for kernel AIO
>
> Signed-off-by: Long Li <longli@...rosoft.com>
> ---
> fs/cifs/cifsfs.h | 1 +
> fs/cifs/cifsglob.h | 5 ++
> fs/cifs/file.c | 210 +++++++++++++++++++++++++++++++++++++++++++++--------
> 3 files changed, 187 insertions(+), 29 deletions(-)
>
> diff --git a/fs/cifs/cifsfs.h b/fs/cifs/cifsfs.h
> index f047e87..ed5479c 100644
> --- a/fs/cifs/cifsfs.h
> +++ b/fs/cifs/cifsfs.h
> @@ -101,6 +101,7 @@ extern int cifs_open(struct inode *inode, struct file *file);
> extern int cifs_close(struct inode *inode, struct file *file);
> extern int cifs_closedir(struct inode *inode, struct file *file);
> extern ssize_t cifs_user_readv(struct kiocb *iocb, struct iov_iter *to);
> +extern ssize_t cifs_direct_readv(struct kiocb *iocb, struct iov_iter *to);
> extern ssize_t cifs_strict_readv(struct kiocb *iocb, struct iov_iter *to);
> extern ssize_t cifs_user_writev(struct kiocb *iocb, struct iov_iter *from);
> extern ssize_t cifs_strict_writev(struct kiocb *iocb, struct iov_iter *from);
> diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
> index 9dcaed0..2131fec 100644
> --- a/fs/cifs/cifsglob.h
> +++ b/fs/cifs/cifsglob.h
> @@ -1172,6 +1172,11 @@ struct cifs_aio_ctx {
> unsigned int len;
> unsigned int total_len;
> bool should_dirty;
> + /*
> + * Indicates if this aio_ctx is for direct_io,
> + * If yes, iter is a copy of the user passed iov_iter
> + */
> + bool direct_io;
> };
>
> struct cifs_readdata;
> diff --git a/fs/cifs/file.c b/fs/cifs/file.c
> index 8d41ca7..6a939fa 100644
> --- a/fs/cifs/file.c
> +++ b/fs/cifs/file.c
> @@ -2965,7 +2965,6 @@ cifs_uncached_readdata_release(struct kref *refcount)
> kref_put(&rdata->ctx->refcount, cifs_aio_ctx_release);
> for (i = 0; i < rdata->nr_pages; i++) {
> put_page(rdata->pages[i]);
> - rdata->pages[i] = NULL;
why is this needed?
> }
> cifs_readdata_release(refcount);
> }
> @@ -3004,7 +3003,7 @@ cifs_readdata_to_iov(struct cifs_readdata *rdata, struct iov_iter *iter)
> return remaining ? -EFAULT : 0;
> }
>
> -static void collect_uncached_read_data(struct cifs_aio_ctx *ctx);
> +static void collect_uncached_read_data(struct cifs_readdata *rdata, struct cifs_aio_ctx *ctx);
>
> static void
> cifs_uncached_readv_complete(struct work_struct *work)
> @@ -3013,7 +3012,7 @@ cifs_uncached_readv_complete(struct work_struct *work)
> struct cifs_readdata, work);
>
> complete(&rdata->done);
> - collect_uncached_read_data(rdata->ctx);
> + collect_uncached_read_data(rdata, rdata->ctx);
> /* the below call can possibly free the last ref to aio ctx */
> kref_put(&rdata->refcount, cifs_uncached_readdata_release);
> }
> @@ -3103,6 +3102,9 @@ cifs_send_async_read(loff_t offset, size_t len, struct cifsFileInfo *open_file,
> int rc;
> pid_t pid;
> struct TCP_Server_Info *server;
> + struct page **pagevec;
> + size_t start;
> + struct iov_iter direct_iov = ctx->iter;
>
> server = tlink_tcon(open_file->tlink)->ses->server;
>
> @@ -3111,6 +3113,9 @@ cifs_send_async_read(loff_t offset, size_t len, struct cifsFileInfo *open_file,
> else
> pid = current->tgid;
>
> + if (ctx->direct_io)
> + iov_iter_advance(&direct_iov, offset - ctx->pos);
> +
> do {
> rc = server->ops->wait_mtu_credits(server, cifs_sb->rsize,
> &rsize, &credits);
> @@ -3118,20 +3123,56 @@ cifs_send_async_read(loff_t offset, size_t len, struct cifsFileInfo *open_file,
> break;
>
> cur_len = min_t(const size_t, len, rsize);
> - npages = DIV_ROUND_UP(cur_len, PAGE_SIZE);
>
> - /* allocate a readdata struct */
> - rdata = cifs_readdata_alloc(npages,
> + if (ctx->direct_io) {
> +
> + cur_len = iov_iter_get_pages_alloc(
> + &direct_iov, &pagevec,
> + cur_len, &start);
> + if (cur_len < 0) {
> + cifs_dbg(VFS,
> + "couldn't get user pages (cur_len=%zd)"
> + " iter type %d"
> + " iov_offset %zd count %zd\n",
> + cur_len, direct_iov.type, direct_iov.iov_offset,
> + direct_iov.count);
> + dump_stack();
> + break;
> + }
> + iov_iter_advance(&direct_iov, cur_len);
> +
> + rdata = cifs_readdata_direct_alloc(
> + pagevec, cifs_uncached_readv_complete);
> + if (!rdata) {
> + add_credits_and_wake_if(server, credits, 0);
> + rc = -ENOMEM;
> + break;
> + }
> +
> + npages = (cur_len + start + PAGE_SIZE-1) / PAGE_SIZE;
> + rdata->page_offset = start;
> + rdata->tailsz = npages > 1 ?
> + cur_len-(PAGE_SIZE-start)-(npages-2)*PAGE_SIZE :
> + cur_len;
> +
> + } else {
> +
> + npages = DIV_ROUND_UP(cur_len, PAGE_SIZE);
> + /* allocate a readdata struct */
> + rdata = cifs_readdata_alloc(npages,
> cifs_uncached_readv_complete);
> - if (!rdata) {
> - add_credits_and_wake_if(server, credits, 0);
> - rc = -ENOMEM;
> - break;
> - }
> + if (!rdata) {
> + add_credits_and_wake_if(server, credits, 0);
> + rc = -ENOMEM;
> + break;
> + }
>
> - rc = cifs_read_allocate_pages(rdata, npages);
> - if (rc)
> - goto error;
> + rc = cifs_read_allocate_pages(rdata, npages);
> + if (rc)
> + goto error;
> +
> + rdata->tailsz = PAGE_SIZE;
> + }
>
> rdata->cfile = cifsFileInfo_get(open_file);
> rdata->nr_pages = npages;
> @@ -3139,7 +3180,6 @@ cifs_send_async_read(loff_t offset, size_t len, struct cifsFileInfo *open_file,
> rdata->bytes = cur_len;
> rdata->pid = pid;
> rdata->pagesz = PAGE_SIZE;
> - rdata->tailsz = PAGE_SIZE;
> rdata->read_into_pages = cifs_uncached_read_into_pages;
> rdata->copy_into_pages = cifs_uncached_copy_into_pages;
> rdata->credits = credits;
> @@ -3153,13 +3193,17 @@ cifs_send_async_read(loff_t offset, size_t len, struct cifsFileInfo *open_file,
> if (rc) {
> add_credits_and_wake_if(server, rdata->credits, 0);
> kref_put(&rdata->refcount,
> - cifs_uncached_readdata_release);
> - if (rc == -EAGAIN)
> + cifs_uncached_readdata_release);
> + if (rc == -EAGAIN) {
> + iov_iter_revert(&direct_iov, cur_len);
> continue;
> + }
> break;
> }
>
> - list_add_tail(&rdata->list, rdata_list);
> + /* Add to aio pending list if it's not there */
> + if (rdata_list)
> + list_add_tail(&rdata->list, rdata_list);
> offset += cur_len;
> len -= cur_len;
> } while (len > 0);
> @@ -3168,7 +3212,7 @@ cifs_send_async_read(loff_t offset, size_t len, struct cifsFileInfo *open_file,
> }
>
> static void
> -collect_uncached_read_data(struct cifs_aio_ctx *ctx)
> +collect_uncached_read_data(struct cifs_readdata *uncached_rdata, struct cifs_aio_ctx *ctx)
Why do you need uncached_rdata argument? It doesn't seem you are using
it in this function.
> {
> struct cifs_readdata *rdata, *tmp;
> struct iov_iter *to = &ctx->iter;
> @@ -3211,10 +3255,12 @@ collect_uncached_read_data(struct cifs_aio_ctx *ctx)
> * reading.
> */
> if (got_bytes && got_bytes < rdata->bytes) {
> - rc = cifs_readdata_to_iov(rdata, to);
> + rc = 0;
> + if (!ctx->direct_io)
> + rc = cifs_readdata_to_iov(rdata, to);
> if (rc) {
> kref_put(&rdata->refcount,
> - cifs_uncached_readdata_release);
> + cifs_uncached_readdata_release);
> continue;
> }
> }
> @@ -3228,28 +3274,32 @@ collect_uncached_read_data(struct cifs_aio_ctx *ctx)
> list_splice(&tmp_list, &ctx->list);
>
> kref_put(&rdata->refcount,
> - cifs_uncached_readdata_release);
> + cifs_uncached_readdata_release);
> goto again;
> } else if (rdata->result)
> rc = rdata->result;
> - else
> + else if (!ctx->direct_io)
> rc = cifs_readdata_to_iov(rdata, to);
>
> /* if there was a short read -- discard anything left */
> if (rdata->got_bytes && rdata->got_bytes < rdata->bytes)
> rc = -ENODATA;
> +
> + ctx->total_len += rdata->got_bytes;
> }
> list_del_init(&rdata->list);
> kref_put(&rdata->refcount, cifs_uncached_readdata_release);
> }
>
> - for (i = 0; i < ctx->npages; i++) {
> - if (ctx->should_dirty)
> - set_page_dirty(ctx->bv[i].bv_page);
> - put_page(ctx->bv[i].bv_page);
> - }
> + if (!ctx->direct_io) {
> + for (i = 0; i < ctx->npages; i++) {
> + if (ctx->should_dirty)
> + set_page_dirty(ctx->bv[i].bv_page);
> + put_page(ctx->bv[i].bv_page);
> + }
>
> - ctx->total_len = ctx->len - iov_iter_count(to);
> + ctx->total_len = ctx->len - iov_iter_count(to);
> + }
>
> cifs_stats_bytes_read(tcon, ctx->total_len);
>
> @@ -3267,6 +3317,108 @@ collect_uncached_read_data(struct cifs_aio_ctx *ctx)
> complete(&ctx->done);
> }
>
> +ssize_t cifs_direct_readv(struct kiocb *iocb, struct iov_iter *to)
> +{
> + size_t len;
> + struct file *file;
> + struct cifs_sb_info *cifs_sb;
> + struct cifsFileInfo *cfile;
> + struct cifs_tcon *tcon;
> + ssize_t rc, total_read = 0;
> + struct TCP_Server_Info *server;
> + loff_t offset = iocb->ki_pos;
> + pid_t pid;
> + struct cifs_aio_ctx *ctx;
> +
> + /*
> + * iov_iter_get_pages_alloc() doesn't work with ITER_KVEC,
> + * fall back to data copy read path
> + * this could be improved by getting pages directly in ITER_KVEC
> + */
> + if (to->type & ITER_KVEC) {
> + cifs_dbg(FYI, "use non-direct cifs_user_readv for kvec I/O\n");
> + return cifs_user_readv(iocb, to);
> + }
> +
> + len = iov_iter_count(to);
> + if (!len)
> + return 0;
> +
> + file = iocb->ki_filp;
> + cifs_sb = CIFS_FILE_SB(file);
> + cfile = file->private_data;
> + tcon = tlink_tcon(cfile->tlink);
> + server = tcon->ses->server;
> +
> + if (!server->ops->async_readv)
> + return -ENOSYS;
> +
> + if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_RWPIDFORWARD)
> + pid = cfile->pid;
> + else
> + pid = current->tgid;
> +
pid variable is not being used.
> + if ((file->f_flags & O_ACCMODE) == O_WRONLY)
> + cifs_dbg(FYI, "attempting read on write only file instance\n");
> +
> + ctx = cifs_aio_ctx_alloc();
> + if (!ctx)
> + return -ENOMEM;
> +
> + ctx->cfile = cifsFileInfo_get(cfile);
> +
> + if (!is_sync_kiocb(iocb))
> + ctx->iocb = iocb;
> +
> + if (to->type == ITER_IOVEC)
> + ctx->should_dirty = true;
> +
> + ctx->pos = offset;
> + ctx->direct_io = true;
> + ctx->iter = *to;
> + ctx->len = len;
> +
> + /* grab a lock here due to read response handlers can access ctx */
> + mutex_lock(&ctx->aio_mutex);
> +
> + rc = cifs_send_async_read(offset, len, cfile, cifs_sb, &ctx->list, ctx);
> +
> + /* if at least one read request send succeeded, then reset rc */
> + if (!list_empty(&ctx->list))
> + rc = 0;
> +
> + mutex_unlock(&ctx->aio_mutex);
> +
> + if (rc) {
> + kref_put(&ctx->refcount, cifs_aio_ctx_release);
> + return rc;
> + }
> +
> + if (!is_sync_kiocb(iocb)) {
> + kref_put(&ctx->refcount, cifs_aio_ctx_release);
> + return -EIOCBQUEUED;
> + }
> +
> + rc = wait_for_completion_killable(&ctx->done);
> + if (rc) {
> + mutex_lock(&ctx->aio_mutex);
> + ctx->rc = rc = -EINTR;
> + total_read = ctx->total_len;
> + mutex_unlock(&ctx->aio_mutex);
> + } else {
> + rc = ctx->rc;
> + total_read = ctx->total_len;
> + }
> +
> + kref_put(&ctx->refcount, cifs_aio_ctx_release);
> +
> + if (total_read) {
> + iocb->ki_pos += total_read;
> + return total_read;
> + }
> + return rc;
This function is almost identical to cifs_user_readv. Can the latter
be refactored to avoid code duplication?
> +}
> +
> ssize_t cifs_user_readv(struct kiocb *iocb, struct iov_iter *to)
> {
> struct file *file = iocb->ki_filp;
> --
> 2.7.4
>
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