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From:   Ilya Dryomov <idryomov@gmail.com>
Date:   Tue, 28 Jan 2020 09:39:49 +0100
Message-ID: <CAOi1vP8sBN6cx+aOtZwJ3FLZHRiZ6_3=cpCD3C5DTRgpE=TmhA@mail.gmail.com>
Subject: Re: [RFC PATCH 2/3] ceph: parallelize all copy-from requests in copy_file_range
To:     Luis Henriques <lhenriques@suse.com>
Cc:     Jeff Layton <jlayton@kernel.org>, Sage Weil <sage@redhat.com>,
        "Yan, Zheng" <zyan@redhat.com>,
        Gregory Farnum <gfarnum@redhat.com>,
        Ceph Development <ceph-devel@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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Sender: linux-kernel-owner@vger.kernel.org
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On Mon, Jan 27, 2020 at 7:44 PM Luis Henriques <lhenriques@suse.com> wrote:
>
> On Mon, Jan 27, 2020 at 06:58:46PM +0100, Ilya Dryomov wrote:
> > On Mon, Jan 27, 2020 at 5:43 PM Luis Henriques <lhenriques@suse.com> wrote:
> > >
> > > Right now the copy_file_range syscall serializes all the OSDs 'copy-from'
> > > operations, waiting for each request to complete before sending the next
> > > one.  This patch modifies copy_file_range so that all the 'copy-from'
> > > operations are sent in bulk and waits for its completion at the end.  This
> > > will allow significant speed-ups, specially when sending requests for
> > > different target OSDs.
> > >
> > > Signed-off-by: Luis Henriques <lhenriques@suse.com>
> > > ---
> > >  fs/ceph/file.c                  | 38 +++++++++++++++++++++++++++++++--
> > >  include/linux/ceph/osd_client.h |  2 ++
> > >  net/ceph/osd_client.c           |  1 +
> > >  3 files changed, 39 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/fs/ceph/file.c b/fs/ceph/file.c
> > > index 1e6cdf2dfe90..5d8f0ba11719 100644
> > > --- a/fs/ceph/file.c
> > > +++ b/fs/ceph/file.c
> > > @@ -1931,6 +1931,28 @@ static int is_file_size_ok(struct inode *src_inode, struct inode *dst_inode,
> > >         return 0;
> > >  }
> > >
> > > +static int wait_copy_from_reqs(struct list_head *osd_reqs)
> > > +{
> > > +       struct ceph_osd_request *req;
> > > +       int ret = 0, err;
> > > +
> > > +       while (!list_empty(osd_reqs)) {
> > > +               req = list_first_entry(osd_reqs,
> > > +                                      struct ceph_osd_request,
> > > +                                      r_copy_item);
> > > +               list_del_init(&req->r_copy_item);
> > > +               err = ceph_osdc_wait_request(req->r_osdc, req);
> > > +               if (err) {
> > > +                       if (!ret)
> > > +                               ret = err;
> > > +                       dout("copy request failed (err=%d)\n", err);
> > > +               }
> > > +               ceph_osdc_put_request(req);
> > > +       }
> > > +
> > > +       return ret;
> > > +}
> >
> > This should probably go into libceph, as ceph_osdc_wait_requests().
>
> Sure, that makes sense.
>
> > > +
> > >  static ssize_t __ceph_copy_file_range(struct file *src_file, loff_t src_off,
> > >                                       struct file *dst_file, loff_t dst_off,
> > >                                       size_t len, unsigned int flags)
> > > @@ -1943,12 +1965,14 @@ static ssize_t __ceph_copy_file_range(struct file *src_file, loff_t src_off,
> > >         struct ceph_fs_client *src_fsc = ceph_inode_to_client(src_inode);
> > >         struct ceph_object_locator src_oloc, dst_oloc;
> > >         struct ceph_object_id src_oid, dst_oid;
> > > +       struct ceph_osd_request *req;
> > >         loff_t endoff = 0, size;
> > >         ssize_t ret = -EIO;
> > >         u64 src_objnum, dst_objnum, src_objoff, dst_objoff;
> > >         u32 src_objlen, dst_objlen, object_size;
> > >         int src_got = 0, dst_got = 0, err, dirty;
> > >         bool do_final_copy = false;
> > > +       LIST_HEAD(osd_reqs);
> > >
> > >         if (src_inode->i_sb != dst_inode->i_sb) {
> > >                 struct ceph_fs_client *dst_fsc = ceph_inode_to_client(dst_inode);
> > > @@ -2097,7 +2121,7 @@ static ssize_t __ceph_copy_file_range(struct file *src_file, loff_t src_off,
> > >                 ceph_oid_printf(&dst_oid, "%llx.%08llx",
> > >                                 dst_ci->i_vino.ino, dst_objnum);
> > >                 /* Do an object remote copy */
> > > -               err = ceph_osdc_copy_from(
> > > +               req = ceph_osdc_copy_from_nowait(
> > >                         &src_fsc->client->osdc,
> > >                         src_ci->i_vino.snap, 0,
> > >                         &src_oid, &src_oloc,
> > > @@ -2108,7 +2132,8 @@ static ssize_t __ceph_copy_file_range(struct file *src_file, loff_t src_off,
> > >                         CEPH_OSD_OP_FLAG_FADVISE_DONTNEED,
> > >                         dst_ci->i_truncate_seq, dst_ci->i_truncate_size,
> > >                         CEPH_OSD_COPY_FROM_FLAG_TRUNCATE_SEQ);
> > > -               if (err) {
> > > +               if (IS_ERR(req)) {
> > > +                       err = PTR_ERR(req);
> > >                         if (err == -EOPNOTSUPP) {
> > >                                 src_fsc->have_copy_from2 = false;
> > >                                 pr_notice("OSDs don't support 'copy-from2'; "
> > > @@ -2117,14 +2142,23 @@ static ssize_t __ceph_copy_file_range(struct file *src_file, loff_t src_off,
> > >                         dout("ceph_osdc_copy_from returned %d\n", err);
> > >                         if (!ret)
> > >                                 ret = err;
> > > +                       /* wait for all queued requests */
> > > +                       wait_copy_from_reqs(&osd_reqs);
> > >                         goto out_caps;
> > >                 }
> > > +               list_add(&req->r_copy_item, &osd_reqs);
> > >                 len -= object_size;
> > >                 src_off += object_size;
> > >                 dst_off += object_size;
> > >                 ret += object_size;
> > >         }
> > >
> > > +       err = wait_copy_from_reqs(&osd_reqs);
> > > +       if (err) {
> > > +               if (!ret)
> > > +                       ret = err;
> > > +               goto out_caps;
> > > +       }
> > >         if (len)
> > >                 /* We still need one final local copy */
> > >                 do_final_copy = true;
> > > diff --git a/include/linux/ceph/osd_client.h b/include/linux/ceph/osd_client.h
> > > index 7916a178d137..2b4a14bc6154 100644
> > > --- a/include/linux/ceph/osd_client.h
> > > +++ b/include/linux/ceph/osd_client.h
> > > @@ -210,6 +210,8 @@ struct ceph_osd_request {
> > >         u64 r_data_offset;                    /* ditto */
> > >         bool r_linger;                        /* don't resend on failure */
> > >
> > > +       struct list_head r_copy_item;         /* used for copy-from operations */
> > > +
> >
> > We have r_private_item for exactly this kind of ad-hoc lists, already
> > used in rbd and ceph_direct_read_write().
>
> Ah!  I've actually considered using it, but thought that using the same
> field for different purposes may be a source of confusion and bugs in the
> future.  But sure, it can be used.  I'll add a comment in the struct
> definition regarding this ad-hoc usage.

It's a means to pass some state through libceph, just like r_priv
pointer.  The comment is already there, it says "for use by callbacks"
meaning that libceph won't touch these fields.

Thanks,

                Ilya