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    SubjectRE: [Patch v4 2/3] CIFS: Add support for direct I/O write
    Date
    > Subject: Re: [Patch v4 2/3] CIFS: Add support for direct I/O write
    >
    > ср, 31 окт. 2018 г. в 15:26, Long Li <longli@linuxonhyperv.com>:
    > >
    > > From: Long Li <longli@microsoft.com>
    > >
    > > With direct I/O write, user supplied buffers are pinned to the memory
    > > and data are transferred directly from user buffers to the transport layer.
    > >
    > > Change in v3: add support for kernel AIO
    > >
    > > Change in v4:
    > > Refactor common write code to __cifs_writev for direct and non-direct I/O.
    > > Retry on direct I/O failure.
    > >
    > > Signed-off-by: Long Li <longli@microsoft.com>
    > > ---
    > > fs/cifs/cifsfs.h | 1 +
    > > fs/cifs/file.c | 194 +++++++++++++++++++++++++++++++++++++++++++----
    > --------
    > > 2 files changed, 154 insertions(+), 41 deletions(-)
    > >
    > > diff --git a/fs/cifs/cifsfs.h b/fs/cifs/cifsfs.h index
    > > 7fba9aa..e9c5103 100644
    > > --- a/fs/cifs/cifsfs.h
    > > +++ b/fs/cifs/cifsfs.h
    > > @@ -105,6 +105,7 @@ 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_direct_writev(struct kiocb *iocb, struct iov_iter
    > > +*from);
    > > extern ssize_t cifs_strict_writev(struct kiocb *iocb, struct iov_iter
    > > *from); extern int cifs_lock(struct file *, int, struct file_lock *);
    > > extern int cifs_fsync(struct file *, loff_t, loff_t, int); diff --git
    > > a/fs/cifs/file.c b/fs/cifs/file.c index daab878..1a41c04 100644
    > > --- a/fs/cifs/file.c
    > > +++ b/fs/cifs/file.c
    > > @@ -2524,6 +2524,55 @@ wdata_fill_from_iovec(struct cifs_writedata
    > > *wdata, struct iov_iter *from, }
    > >
    > > static int
    > > +cifs_resend_wdata(struct cifs_writedata *wdata, struct list_head
    > > +*wdata_list, struct cifs_aio_ctx *ctx) {
    > > + int wait_retry = 0;
    > > + unsigned int wsize, credits;
    > > + int rc;
    > > + struct TCP_Server_Info *server =
    > > +tlink_tcon(wdata->cfile->tlink)->ses->server;
    > > +
    > > + /*
    > > + * Try to resend this wdata, waiting for credits up to 3 seconds.
    > > + * Note: we are attempting to resend the whole wdata not in
    > segments
    > > + */
    > > + do {
    > > + rc = server->ops->wait_mtu_credits(server,
    > > + wdata->bytes, &wsize, &credits);
    > > +
    > > + if (rc)
    > > + break;
    > > +
    > > + if (wsize < wdata->bytes) {
    > > + add_credits_and_wake_if(server, credits, 0);
    > > + msleep(1000);
    > > + wait_retry++;
    > > + }
    > > + } while (wsize < wdata->bytes && wait_retry < 3);
    > > +
    > > + if (wsize < wdata->bytes) {
    > > + rc = -EBUSY;
    > > + goto out;
    > > + }
    > > +
    > > + rc = -EAGAIN;
    > > + while (rc == -EAGAIN)
    > > + if (!wdata->cfile->invalidHandle ||
    > > + !(rc = cifs_reopen_file(wdata->cfile, false)))
    > > + rc = server->ops->async_writev(wdata,
    > > +
    > > + cifs_uncached_writedata_release);
    > > +
    > > + if (!rc) {
    > > + list_add_tail(&wdata->list, wdata_list);
    > > + return 0;
    > > + }
    > > +
    > > + add_credits_and_wake_if(server, wdata->credits, 0);
    > > +out:
    > > + kref_put(&wdata->refcount, cifs_uncached_writedata_release);
    > > +
    > > + return rc;
    > > +}
    > > +
    > > +static int
    > > cifs_write_from_iter(loff_t offset, size_t len, struct iov_iter *from,
    > > struct cifsFileInfo *open_file,
    > > struct cifs_sb_info *cifs_sb, struct list_head
    > > *wdata_list, @@ -2537,6 +2586,8 @@ cifs_write_from_iter(loff_t offset,
    > size_t len, struct iov_iter *from,
    > > loff_t saved_offset = offset;
    > > pid_t pid;
    > > struct TCP_Server_Info *server;
    > > + struct page **pagevec;
    > > + size_t start;
    > >
    > > if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_RWPIDFORWARD)
    > > pid = open_file->pid;
    > > @@ -2553,38 +2604,74 @@ cifs_write_from_iter(loff_t offset, size_t len,
    > struct iov_iter *from,
    > > if (rc)
    > > break;
    > >
    > > - nr_pages = get_numpages(wsize, len, &cur_len);
    > > - wdata = cifs_writedata_alloc(nr_pages,
    > > + if (ctx->direct_io) {
    > > + cur_len = iov_iter_get_pages_alloc(
    > > + from, &pagevec, wsize, &start);
    > > + if (cur_len < 0) {
    > > + cifs_dbg(VFS,
    > > + "direct_writev couldn't get user pages "
    > > + "(rc=%zd) iter type %d iov_offset %zd count"
    > > + " %zd\n",
    > > + cur_len, from->type,
    > > + from->iov_offset, from->count);
    > > + dump_stack();
    > > + break;
    > > + }
    > > + iov_iter_advance(from, cur_len);
    > > +
    > > + nr_pages = (cur_len + start + PAGE_SIZE - 1) /
    > > + PAGE_SIZE;
    > > +
    > > + wdata = cifs_writedata_direct_alloc(pagevec,
    > > cifs_uncached_writev_complete);
    > > - if (!wdata) {
    > > - rc = -ENOMEM;
    > > - add_credits_and_wake_if(server, credits, 0);
    > > - break;
    > > - }
    > > + if (!wdata) {
    > > + rc = -ENOMEM;
    > > + add_credits_and_wake_if(server, credits, 0);
    > > + break;
    > > + }
    > >
    > > - rc = cifs_write_allocate_pages(wdata->pages, nr_pages);
    > > - if (rc) {
    > > - kfree(wdata);
    > > - add_credits_and_wake_if(server, credits, 0);
    > > - break;
    > > - }
    > >
    > > - num_pages = nr_pages;
    > > - rc = wdata_fill_from_iovec(wdata, from, &cur_len, &num_pages);
    > > - if (rc) {
    > > - for (i = 0; i < nr_pages; i++)
    > > - put_page(wdata->pages[i]);
    > > - kfree(wdata);
    > > - add_credits_and_wake_if(server, credits, 0);
    > > - break;
    > > - }
    > > + wdata->page_offset = start;
    > > + wdata->tailsz =
    > > + nr_pages > 1 ?
    > > + cur_len - (PAGE_SIZE - start) -
    > > + (nr_pages - 2) * PAGE_SIZE :
    > > + cur_len;
    > > + } else {
    > > + nr_pages = get_numpages(wsize, len, &cur_len);
    > > + wdata = cifs_writedata_alloc(nr_pages,
    > > + cifs_uncached_writev_complete);
    > > + if (!wdata) {
    > > + rc = -ENOMEM;
    > > + add_credits_and_wake_if(server, credits, 0);
    > > + break;
    > > + }
    > >
    > > - /*
    > > - * Bring nr_pages down to the number of pages we actually used,
    > > - * and free any pages that we didn't use.
    > > - */
    > > - for ( ; nr_pages > num_pages; nr_pages--)
    > > - put_page(wdata->pages[nr_pages - 1]);
    > > + rc = cifs_write_allocate_pages(wdata->pages, nr_pages);
    > > + if (rc) {
    > > + kfree(wdata);
    > > + add_credits_and_wake_if(server, credits, 0);
    > > + break;
    > > + }
    > > +
    > > + num_pages = nr_pages;
    > > + rc = wdata_fill_from_iovec(wdata, from, &cur_len,
    > &num_pages);
    > > + if (rc) {
    > > + for (i = 0; i < nr_pages; i++)
    > > + put_page(wdata->pages[i]);
    > > + kfree(wdata);
    > > + add_credits_and_wake_if(server, credits, 0);
    > > + break;
    > > + }
    > > +
    > > + /*
    > > + * Bring nr_pages down to the number of pages we actually
    > used,
    > > + * and free any pages that we didn't use.
    > > + */
    > > + for ( ; nr_pages > num_pages; nr_pages--)
    > > + put_page(wdata->pages[nr_pages - 1]);
    > > +
    > > + wdata->tailsz = cur_len - ((nr_pages - 1) * PAGE_SIZE);
    > > + }
    > >
    > > wdata->sync_mode = WB_SYNC_ALL;
    > > wdata->nr_pages = nr_pages; @@ -2593,7 +2680,6 @@
    > > cifs_write_from_iter(loff_t offset, size_t len, struct iov_iter *from,
    > > wdata->pid = pid;
    > > wdata->bytes = cur_len;
    > > wdata->pagesz = PAGE_SIZE;
    > > - wdata->tailsz = cur_len - ((nr_pages - 1) * PAGE_SIZE);
    > > wdata->credits = credits;
    > > wdata->ctx = ctx;
    > > kref_get(&ctx->refcount); @@ -2668,13 +2754,17 @@
    > > static void collect_uncached_write_data(struct cifs_aio_ctx *ctx)
    > > INIT_LIST_HEAD(&tmp_list);
    > > list_del_init(&wdata->list);
    > >
    > > - iov_iter_advance(&tmp_from,
    > > + if (ctx->direct_io)
    > > + rc = cifs_resend_wdata(wdata, &tmp_list, ctx);
    > > + else {
    > > + iov_iter_advance(&tmp_from,
    > > wdata->offset -
    > > ctx->pos);
    > >
    > > - rc = cifs_write_from_iter(wdata->offset,
    > > + rc =
    > > + cifs_write_from_iter(wdata->offset,
    > > wdata->bytes, &tmp_from,
    > > ctx->cfile, cifs_sb, &tmp_list,
    > > ctx);
    > > + }
    > >
    > > list_splice(&tmp_list, &ctx->list);
    > >
    > > @@ -2687,8 +2777,9 @@ static void collect_uncached_write_data(struct
    > cifs_aio_ctx *ctx)
    > > kref_put(&wdata->refcount, cifs_uncached_writedata_release);
    > > }
    > >
    > > - for (i = 0; i < ctx->npages; i++)
    > > - put_page(ctx->bv[i].bv_page);
    > > + if (!ctx->direct_io)
    > > + for (i = 0; i < ctx->npages; i++)
    > > + put_page(ctx->bv[i].bv_page);
    > >
    > > cifs_stats_bytes_written(tcon, ctx->total_len);
    > > set_bit(CIFS_INO_INVALID_MAPPING,
    > > &CIFS_I(dentry->d_inode)->flags); @@ -2703,7 +2794,7 @@ static void
    > collect_uncached_write_data(struct cifs_aio_ctx *ctx)
    > > complete(&ctx->done);
    > > }
    > >
    > > -ssize_t cifs_user_writev(struct kiocb *iocb, struct iov_iter *from)
    > > +static ssize_t __cifs_writev(struct kiocb *iocb, struct iov_iter
    > > +*from, bool direct)
    > > {
    > > struct file *file = iocb->ki_filp;
    > > ssize_t total_written = 0;
    > > @@ -2712,13 +2803,18 @@ ssize_t cifs_user_writev(struct kiocb *iocb,
    > struct iov_iter *from)
    > > struct cifs_sb_info *cifs_sb;
    > > struct cifs_aio_ctx *ctx;
    > > struct iov_iter saved_from = *from;
    > > + size_t len = iov_iter_count(from);
    > > int rc;
    > >
    > > /*
    > > - * BB - optimize the way when signing is disabled. We can drop this
    > > - * extra memory-to-memory copying and use iovec buffers for
    > constructing
    > > - * write request.
    > > + * iov_iter_get_pages_alloc doesn't work with ITER_KVEC.
    > > + * In this case, fall back to non-direct write function.
    > > + * this could be improved by getting pages directly in
    > > + ITER_KVEC
    > > */
    > > + if (direct && from->type & ITER_KVEC) {
    > > + cifs_dbg(FYI, "use non-direct cifs_writev for kvec I/O\n");
    > > + direct = false;
    > > + }
    > >
    > > rc = generic_write_checks(iocb, from);
    > > if (rc <= 0)
    > > @@ -2742,10 +2838,16 @@ ssize_t cifs_user_writev(struct kiocb *iocb,
    > > struct iov_iter *from)
    > >
    > > ctx->pos = iocb->ki_pos;
    > >
    > > - rc = setup_aio_ctx_iter(ctx, from, WRITE);
    > > - if (rc) {
    > > - kref_put(&ctx->refcount, cifs_aio_ctx_release);
    > > - return rc;
    > > + if (direct) {
    > > + ctx->direct_io = true;
    > > + ctx->iter = *from;
    > > + ctx->len = len;
    > > + } else {
    > > + rc = setup_aio_ctx_iter(ctx, from, WRITE);
    > > + if (rc) {
    > > + kref_put(&ctx->refcount, cifs_aio_ctx_release);
    > > + return rc;
    > > + }
    > > }
    > >
    > > /* grab a lock here due to read response handlers can access
    > > ctx */ @@ -2795,6 +2897,16 @@ ssize_t cifs_user_writev(struct kiocb
    > *iocb, struct iov_iter *from)
    > > return total_written;
    > > }
    > >
    > > +ssize_t cifs_direct_writev(struct kiocb *iocb, struct iov_iter *from)
    > > +{
    > > + return __cifs_writev(iocb, from, true); }
    > > +
    > > +ssize_t cifs_user_writev(struct kiocb *iocb, struct iov_iter *from) {
    > > + return __cifs_writev(iocb, from, false); }
    > > +
    > > static ssize_t
    > > cifs_writev(struct kiocb *iocb, struct iov_iter *from) {
    > > --
    > > 2.7.4
    > >
    >
    > Did you measure the performance benefit of using O_DIRECT with your
    > patches for non-RDMA mode?

    Here are some of the results measured on TCP/IP over IPoIB 40G Infiniband. Please note that IPoIB is done in software so it's slower than a 40G Ethernet NIC.

    All servers are running 2 X Intel(R) Xeon(R) CPU E5-2650 v3 @ 2.30GHz. Tested on FIO 64k read or write with queue depths 1 or 16. All the tests are running with 1 FIO job, and with "direct=1".

    Without direct I/O:
    read 64k d1 113669KB/s
    read 64k d16 618428KB/s
    write 64k d1 134911KB/s
    write 64k d16 457005KB/s

    With direct I/O:
    read 64k d1 127134KB/s
    read 64k d16 714629KB/s
    write 64k d1 129268KB/s
    write 64k d16 461054KB/s

    Direct I/O improvement:
    read 64k d1 11%
    read 64k d16 15%
    write 64k d1 -5%
    write 64k d16 1%



    >
    > --
    > Best regards,
    > Pavel Shilovsky
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