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From:   Pavel Shilovsky <piastryyy@gmail.com>
Date:   Thu, 29 Nov 2018 10:31:08 -0800
Message-ID: <CAKywueSwidw-71FkpLY1w+fzHL6h85qi69uOC-B04GNY6XsZaA@mail.gmail.com>
Subject: Re: [Patch v4 2/3] CIFS: Add support for direct I/O write
To:     Long Li <longli@microsoft.com>
Cc:     Steve French <sfrench@samba.org>,
        linux-cifs <linux-cifs@vger.kernel.org>,
        samba-technical <samba-technical@lists.samba.org>,
        Kernel Mailing List <linux-kernel@vger.kernel.org>
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Sender: linux-kernel-owner@vger.kernel.org
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=D1=81=D1=80, 28 =D0=BD=D0=BE=D1=8F=D0=B1. 2018 =D0=B3. =D0=B2 18:20, Long =
Li <longli@microsoft.com>:
>
> > Subject: Re: [Patch v4 2/3] CIFS: Add support for direct I/O write
> >
> > =D1=81=D1=80, 31 =D0=BE=D0=BA=D1=82. 2018 =D0=B3. =D0=B2 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_ite=
r
> > > +*from);
> > >  extern ssize_t cifs_strict_writev(struct kiocb *iocb, struct iov_ite=
r
> > > *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 =3D 0;
> > > +       unsigned int wsize, credits;
> > > +       int rc;
> > > +       struct TCP_Server_Info *server =3D
> > > +tlink_tcon(wdata->cfile->tlink)->ses->server;
> > > +
> > > +       /*
> > > +        * Try to resend this wdata, waiting for credits up to 3 seco=
nds.
> > > +        * Note: we are attempting to resend the whole wdata not in
> > segments
> > > +        */
> > > +       do {
> > > +               rc =3D 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 =3D -EBUSY;
> > > +               goto out;
> > > +       }
> > > +
> > > +       rc =3D -EAGAIN;
> > > +       while (rc =3D=3D -EAGAIN)
> > > +               if (!wdata->cfile->invalidHandle ||
> > > +                   !(rc =3D cifs_reopen_file(wdata->cfile, false)))
> > > +                       rc =3D 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 *fro=
m,
> > >                      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 =3D 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 =3D open_file->pid;
> > > @@ -2553,38 +2604,74 @@ cifs_write_from_iter(loff_t offset, size_t le=
n,
> > struct iov_iter *from,
> > >                 if (rc)
> > >                         break;
> > >
> > > -               nr_pages =3D get_numpages(wsize, len, &cur_len);
> > > -               wdata =3D cifs_writedata_alloc(nr_pages,
> > > +               if (ctx->direct_io) {
> > > +                       cur_len =3D iov_iter_get_pages_alloc(
> > > +                               from, &pagevec, wsize, &start);
> > > +                       if (cur_len < 0) {
> > > +                               cifs_dbg(VFS,
> > > +                                       "direct_writev couldn't get u=
ser pages "
> > > +                                       "(rc=3D%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 =3D (cur_len + start + PAGE_SIZE - 1=
) /
> > > + PAGE_SIZE;
> > > +
> > > +                       wdata =3D cifs_writedata_direct_alloc(pagevec=
,
> > >                                              cifs_uncached_writev_com=
plete);
> > > -               if (!wdata) {
> > > -                       rc =3D -ENOMEM;
> > > -                       add_credits_and_wake_if(server, credits, 0);
> > > -                       break;
> > > -               }
> > > +                       if (!wdata) {
> > > +                               rc =3D -ENOMEM;
> > > +                               add_credits_and_wake_if(server, credi=
ts, 0);
> > > +                               break;
> > > +                       }
> > >
> > > -               rc =3D cifs_write_allocate_pages(wdata->pages, nr_pag=
es);
> > > -               if (rc) {
> > > -                       kfree(wdata);
> > > -                       add_credits_and_wake_if(server, credits, 0);
> > > -                       break;
> > > -               }
> > >
> > > -               num_pages =3D nr_pages;
> > > -               rc =3D wdata_fill_from_iovec(wdata, from, &cur_len, &=
num_pages);
> > > -               if (rc) {
> > > -                       for (i =3D 0; i < nr_pages; i++)
> > > -                               put_page(wdata->pages[i]);
> > > -                       kfree(wdata);
> > > -                       add_credits_and_wake_if(server, credits, 0);
> > > -                       break;
> > > -               }
> > > +                       wdata->page_offset =3D start;
> > > +                       wdata->tailsz =3D
> > > +                               nr_pages > 1 ?
> > > +                                       cur_len - (PAGE_SIZE - start)=
 -
> > > +                                       (nr_pages - 2) * PAGE_SIZE :
> > > +                                       cur_len;
> > > +               } else {
> > > +                       nr_pages =3D get_numpages(wsize, len, &cur_le=
n);
> > > +                       wdata =3D cifs_writedata_alloc(nr_pages,
> > > +                                            cifs_uncached_writev_com=
plete);
> > > +                       if (!wdata) {
> > > +                               rc =3D -ENOMEM;
> > > +                               add_credits_and_wake_if(server, credi=
ts, 0);
> > > +                               break;
> > > +                       }
> > >
> > > -               /*
> > > -                * Bring nr_pages down to the number of pages we actu=
ally 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 =3D cifs_write_allocate_pages(wdata->pages=
, nr_pages);
> > > +                       if (rc) {
> > > +                               kfree(wdata);
> > > +                               add_credits_and_wake_if(server, credi=
ts, 0);
> > > +                               break;
> > > +                       }
> > > +
> > > +                       num_pages =3D nr_pages;
> > > +                       rc =3D wdata_fill_from_iovec(wdata, from, &cu=
r_len,
> > &num_pages);
> > > +                       if (rc) {
> > > +                               for (i =3D 0; i < nr_pages; i++)
> > > +                                       put_page(wdata->pages[i]);
> > > +                               kfree(wdata);
> > > +                               add_credits_and_wake_if(server, credi=
ts, 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 =3D cur_len - ((nr_pages - 1) *=
 PAGE_SIZE);
> > > +               }
> > >
> > >                 wdata->sync_mode =3D WB_SYNC_ALL;
> > >                 wdata->nr_pages =3D nr_pages; @@ -2593,7 +2680,6 @@
> > > cifs_write_from_iter(loff_t offset, size_t len, struct iov_iter *from=
,
> > >                 wdata->pid =3D pid;
> > >                 wdata->bytes =3D cur_len;
> > >                 wdata->pagesz =3D PAGE_SIZE;
> > > -               wdata->tailsz =3D cur_len - ((nr_pages - 1) * PAGE_SI=
ZE);
> > >                 wdata->credits =3D credits;
> > >                 wdata->ctx =3D 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 =3D cifs_resend_wdata(wdat=
a, &tmp_list, ctx);
> > > +                               else {
> > > +                                       iov_iter_advance(&tmp_from,
> > >                                                  wdata->offset -
> > > ctx->pos);
> > >
> > > -                               rc =3D cifs_write_from_iter(wdata->of=
fset,
> > > +                                       rc =3D
> > > + cifs_write_from_iter(wdata->offset,
> > >                                                 wdata->bytes, &tmp_fr=
om,
> > >                                                 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_re=
lease);
> > >         }
> > >
> > > -       for (i =3D 0; i < ctx->npages; i++)
> > > -               put_page(ctx->bv[i].bv_page);
> > > +       if (!ctx->direct_io)
> > > +               for (i =3D 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 =3D iocb->ki_filp;
> > >         ssize_t total_written =3D 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 =3D *from;
> > > +       size_t len =3D iov_iter_count(from);
> > >         int rc;
> > >
> > >         /*
> > > -        * BB - optimize the way when signing is disabled. We can dro=
p 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 =3D false;
> > > +       }
> > >
> > >         rc =3D generic_write_checks(iocb, from);
> > >         if (rc <=3D 0)
> > > @@ -2742,10 +2838,16 @@ ssize_t cifs_user_writev(struct kiocb *iocb,
> > > struct iov_iter *from)
> > >
> > >         ctx->pos =3D iocb->ki_pos;
> > >
> > > -       rc =3D setup_aio_ctx_iter(ctx, from, WRITE);
> > > -       if (rc) {
> > > -               kref_put(&ctx->refcount, cifs_aio_ctx_release);
> > > -               return rc;
> > > +       if (direct) {
> > > +               ctx->direct_io =3D true;
> > > +               ctx->iter =3D *from;
> > > +               ctx->len =3D len;
> > > +       } else {
> > > +               rc =3D 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 Ethe=
rnet NIC.
>
> All servers are running 2 X Intel(R) Xeon(R) CPU E5-2650 v3 @ 2.30GHz. Te=
sted on FIO 64k read or write with queue depths 1 or 16. All the tests are =
running with 1 FIO job, and with "direct=3D1".
>
> 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%
                      ^^^
This is strange. Is it consistent across multiple runs?

> write 64k d16   1%

Good read performance improvements overall and it seems write
performance results need more investigations.

--
Best regards,
Pavel Shilovsky