RE: [PATCH V3 (resend) 3/7] CIFS: Add support for direct I/O read

From: Long Li
Date: Mon Sep 24 2018 - 14:39:53 EST

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> Subject: Re: [PATCH V3 (resend) 3/7] CIFS: Add support for direct I/O read
>
> ÑÑ, 20 ÑÐÐÑ. 2018 Ð. Ð 14:22, 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
> >
> > Signed-off-by: Long Li <longli@xxxxxxxxxxxxx>
> > ---
> > 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?
It is not needed. But there is no need to set pages[i] to NULL, so just remove this.
>
> > }
> > 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.

My bad. I will remove it.

>
> > {
> > 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.

I will remove it.

>
> > + 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?

I was thinking about the same thing. I will merge them into one function.

>
> > +}
> > +
> > 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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