Re: [Patch v4 1/3] CIFS: Add support for direct I/O read

From: Pavel Shilovsky
Date: Fri Nov 16 2018 - 19:17:32 EST

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Hi Long,

Please find my comments below.

ÑÑ, 31 ÐÐÑ. 2018 Ð. Ð 15:14, Long Li <longli@xxxxxxxxxxxxxxxxx>:
>
> From: Long Li <longli@xxxxxxxxxxxxx>
>
> 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
>
> Change in v4:
> Refactor common read code to __cifs_readv for direct and non-direct I/O.
> Retry on direct I/O failure.
>
> Signed-off-by: Long Li <longli@xxxxxxxxxxxxx>
> ---
> fs/cifs/cifsfs.h | 1 +
> fs/cifs/cifsglob.h | 5 ++
> fs/cifs/file.c | 219 +++++++++++++++++++++++++++++++++++++++++++----------
> 3 files changed, 186 insertions(+), 39 deletions(-)
>
> diff --git a/fs/cifs/cifsfs.h b/fs/cifs/cifsfs.h
> index 5f02318..7fba9aa 100644
> --- a/fs/cifs/cifsfs.h
> +++ b/fs/cifs/cifsfs.h
> @@ -102,6 +102,7 @@ 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 7f62c98..52248dd 100644
> --- a/fs/cifs/cifsglob.h
> +++ b/fs/cifs/cifsglob.h
> @@ -1146,6 +1146,11 @@ 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 87eece6..daab878 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;
> }
> cifs_readdata_release(refcount);
> }
> @@ -3092,6 +3091,63 @@ cifs_uncached_copy_into_pages(struct TCP_Server_Info *server,
> return uncached_fill_pages(server, rdata, iter, iter->count);
> }
>
> +static int cifs_resend_rdata(struct cifs_readdata *rdata,
> + struct list_head *rdata_list,
> + struct cifs_aio_ctx *ctx)
> +{
> + int wait_retry = 0;
> + unsigned int rsize, credits;
> + int rc;
> + struct TCP_Server_Info *server = tlink_tcon(rdata->cfile->tlink)->ses->server;
> +
> + /*
> + * Try to resend this rdata, waiting for credits up to 3 seconds.
> + * Note: we are attempting to resend the whole rdata not in segments
> + */
> + do {
> + rc = server->ops->wait_mtu_credits(server, rdata->bytes,
> + &rsize, &credits);
> +
> + if (rc)
> + break;
> +
> + if (rsize < rdata->bytes) {
> + add_credits_and_wake_if(server, credits, 0);
> + msleep(1000);
> + wait_retry++;
> + }
> + } while (rsize < rdata->bytes && wait_retry < 3);
> +
> + /*
> + * If we can't find enough credits to send this rdata
> + * release the rdata and return failure, this will pass
> + * whatever I/O amount we have finished to VFS.
> + */
> + if (rsize < rdata->bytes) {
> + rc = -EBUSY;

We don't have enough credits and return EBUSY here...

> + goto out;
> + }
> +
> + rc = -EAGAIN;
> + while (rc == -EAGAIN)
> + if (!rdata->cfile->invalidHandle ||
> + !(rc = cifs_reopen_file(rdata->cfile, true)))
> + rc = server->ops->async_readv(rdata);
> +
> + if (!rc) {
> + /* Add to aio pending list */
> + list_add_tail(&rdata->list, rdata_list);
> + return 0;
> + }
> +
> + add_credits_and_wake_if(server, rdata->credits, 0);
> +out:
> + kref_put(&rdata->refcount,
> + cifs_uncached_readdata_release);
> +
> + return rc;
> +}
> +
> static int
> cifs_send_async_read(loff_t offset, size_t len, struct cifsFileInfo *open_file,
> struct cifs_sb_info *cifs_sb, struct list_head *rdata_list,
> @@ -3103,6 +3159,9 @@ 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 +3170,9 @@ 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 +3180,56 @@ 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 +3237,6 @@ 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;
> @@ -3153,9 +3250,11 @@ 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;
> }
>
> @@ -3211,45 +3310,62 @@ 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;
> }
> }
>
> - rc = cifs_send_async_read(
> + if (ctx->direct_io) {
> + /*
> + * Re-use rdata as this is a
> + * direct I/O
> + */
> + rc = cifs_resend_rdata(
> + rdata,
> + &tmp_list, ctx);

...so we set rc to -EBUSY...

> + } else {
> + rc = cifs_send_async_read(
> rdata->offset + got_bytes,
> rdata->bytes - got_bytes,
> rdata->cfile, cifs_sb,
> &tmp_list, ctx);
>
> + kref_put(&rdata->refcount,
> + cifs_uncached_readdata_release);
> + }
> +
> list_splice(&tmp_list, &ctx->list);
>
> - kref_put(&rdata->refcount,
> - 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);
>
> @@ -3267,18 +3383,27 @@ collect_uncached_read_data(struct cifs_aio_ctx *ctx)
> complete(&ctx->done);

and then ctx->rc is set to -EBUSY too.

> }
>
> -ssize_t cifs_user_readv(struct kiocb *iocb, struct iov_iter *to)
> +ssize_t __cifs_readv(struct kiocb *iocb, struct iov_iter *to, bool direct)
> {
> - struct file *file = iocb->ki_filp;
> - ssize_t rc;
> size_t len;
> - ssize_t total_read = 0;
> - loff_t offset = iocb->ki_pos;
> + struct file *file = iocb->ki_filp;
> struct cifs_sb_info *cifs_sb;
> - struct cifs_tcon *tcon;
> struct cifsFileInfo *cfile;
> + struct cifs_tcon *tcon;
> + ssize_t rc, total_read = 0;
> + loff_t offset = iocb->ki_pos;
> 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 (direct && to->type & ITER_KVEC) {
> + cifs_dbg(FYI, "use non-direct cifs_user_readv for kvec I/O\n");
> + direct = false;
> + }
> +
> len = iov_iter_count(to);
> if (!len)
> return 0;
> @@ -3305,14 +3430,20 @@ ssize_t cifs_user_readv(struct kiocb *iocb, struct iov_iter *to)
> if (to->type == ITER_IOVEC)
> ctx->should_dirty = true;
>
> - rc = setup_aio_ctx_iter(ctx, to, READ);
> - if (rc) {
> - kref_put(&ctx->refcount, cifs_aio_ctx_release);
> - return rc;
> + if (direct) {
> + ctx->pos = offset;
> + ctx->direct_io = true;
> + ctx->iter = *to;
> + ctx->len = len;
> + } else {
> + rc = setup_aio_ctx_iter(ctx, to, READ);
> + if (rc) {
> + kref_put(&ctx->refcount, cifs_aio_ctx_release);
> + return rc;
> + }
> + len = ctx->len;
> }
>
> - len = ctx->len;
> -
> /* grab a lock here due to read response handlers can access ctx */
> mutex_lock(&ctx->aio_mutex);
>
> @@ -3354,6 +3485,16 @@ ssize_t cifs_user_readv(struct kiocb *iocb, struct iov_iter *to)
> return rc;

In case of a blocking read we will return -EBUSY to the caller but
read man page doesn't say anything about a possibility to return this
error code. Is it being mapped somehow by VFS or is there another
consideration? The same question applies to the write patch as well.

> }
>
> +ssize_t cifs_direct_readv(struct kiocb *iocb, struct iov_iter *to)
> +{
> + return __cifs_readv(iocb, to, true);
> +}
> +
> +ssize_t cifs_user_readv(struct kiocb *iocb, struct iov_iter *to)
> +{
> + return __cifs_readv(iocb, to, false);
> +}
> +
> ssize_t
> cifs_strict_readv(struct kiocb *iocb, struct iov_iter *to)
> {
> --
> 2.7.4
>

--
Best regards,
Pavel Shilovsky

Next message: Eric Biggers: "Re: [RFC PATCH v3 10/15] crypto: poly1305 - use structures for key and accumulator"
Previous message: Jolly Shah: "[PATCH 0/9] dt-bindings: Firmware node binding for ZynqMP core"
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