Re: [RFC PATCH 2/3] ceph: parallelize all copy-from requests in copy_file_range

From: Ilya Dryomov
Date: Tue Jan 28 2020 - 03:39:45 EST

On Mon, Jan 27, 2020 at 7:44 PM Luis Henriques <lhenriques@xxxxxxxx> 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@xxxxxxxx> 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@xxxxxxxx>
> > > ---
> > > 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