Re: [PATCH 1/1] ceph: parallelize all copy-from requests in copy_file_range

[Luis Henriques <lhenriques@suse.com>]

On Thu, Jan 30, 2020 at 03:15:52PM +0100, Ilya Dryomov wrote:
> On Wed, Jan 29, 2020 at 7:20 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 wait for its completion at the end.  This
> > will allow significant speed-ups, specially when sending requests to
> > different target OSDs.
> >
> > There's also a throttling mechanism so that OSDs aren't flooded with
> > requests when a client performs a big file copy.  Currently the throttling
> > mechanism simply waits for the requests when the number of in-flight
> > requests reaches (wsize / object size) * 4.
> >
> > Signed-off-by: Luis Henriques <lhenriques@suse.com>
> > ---
> >  fs/ceph/file.c                  | 34 ++++++++++++++++++++--
> >  include/linux/ceph/osd_client.h |  5 +++-
> >  net/ceph/osd_client.c           | 50 ++++++++++++++++++++++++---------
> >  3 files changed, 72 insertions(+), 17 deletions(-)
> >
> > diff --git a/fs/ceph/file.c b/fs/ceph/file.c
> > index 1e6cdf2dfe90..77a16324dcb4 100644
> > --- a/fs/ceph/file.c
> > +++ b/fs/ceph/file.c
> > @@ -1943,12 +1943,14 @@ 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;
> > +       int src_got = 0, dst_got = 0, err, dirty, ncopies;
> >         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);
> > @@ -2083,6 +2085,12 @@ static ssize_t __ceph_copy_file_range(struct file *src_file, loff_t src_off,
> >                         goto out_caps;
> >         }
> >         object_size = src_ci->i_layout.object_size;
> > +
> > +       /*
> > +        * Throttle the object copies: ncopies holds the number of allowed
> > +        * in-flight 'copy-from' requests before waiting for their completion
> > +        */
> > +       ncopies = (src_fsc->mount_options->wsize / object_size) * 4;
> >         while (len >= object_size) {
> >                 ceph_calc_file_object_mapping(&src_ci->i_layout, src_off,
> >                                               object_size, &src_objnum,
> > @@ -2097,7 +2105,7 @@ 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(
> >                         &src_fsc->client->osdc,
> >                         src_ci->i_vino.snap, 0,
> >                         &src_oid, &src_oloc,
> > @@ -2108,7 +2116,8 @@ 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) {
> 
> No point in checking for EOPNOTSUPP here, because ceph_osdc_copy_from()
> won't ever return that.  This loop needs more massaging and more testing
> on old OSDs...

Right, I missed that.  Setting src_fsc->have_copy_from2 to false should be
moved into the two 'if (err)' statements following the calls to
ceph_osdc_wait_requests.  I'll go fix that.  And test it with on a cluster
with OSDs that don't have this copy-from2 operation.

> >                                 src_fsc->have_copy_from2 = false;
> >                                 pr_notice("OSDs don't support 'copy-from2'; "
> > @@ -2117,14 +2126,33 @@ 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 */
> > +                       ceph_osdc_wait_requests(&osd_reqs);
> >                         goto out_caps;
> >                 }
> > +               list_add(&req->r_private_item, &osd_reqs);
> >                 len -= object_size;
> >                 src_off += object_size;
> >                 dst_off += object_size;
> >                 ret += object_size;
> 
> So ret is incremented here, but you have numerious tests where ret is
> assigned an error only if ret is 0.  Unless I'm missing something, this
> interferes with returning errors from __ceph_copy_file_range().

Well, the problem is that an error may occur *after* we have already done
some copies.  In that case we need to return the number of bytes that have
been successfully copied instead of an error; eventually, subsequent calls
to complete the copy_file_range will then return the error.  At least this
is how I understood the man page (i.e. similar to the write(2) syscall).

> > +               if (--ncopies == 0) {
> > +                       err = ceph_osdc_wait_requests(&osd_reqs);
> > +                       if (err) {
> > +                               if (!ret)
> > +                                       ret = err;
> > +                               goto out_caps;
> > +                       }
> > +                       ncopies = (src_fsc->mount_options->wsize /
> > +                                  object_size) * 4;
> 
> The object size is constant within a file, so ncopies should be too.
> Perhaps introduce a counter instead of recalculating ncopies here?

Not sure I understood your comment.  You would rather have:

 * ncopies initialized only once outside the loop
 * have a counter counting the number of objects copied
 * call ceph_osdc_wait_requests() when this counter is a multiple of
   ncopies

Is that it?

Cheers,
--
Luís

> > +               }
> >         }
> >
> > +       err = ceph_osdc_wait_requests(&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 5a62dbd3f4c2..25565dbfd65a 100644
> > --- a/include/linux/ceph/osd_client.h
> > +++ b/include/linux/ceph/osd_client.h
> > @@ -526,7 +526,8 @@ extern int ceph_osdc_writepages(struct ceph_osd_client *osdc,
> >                                 struct timespec64 *mtime,
> >                                 struct page **pages, int nr_pages);
> >
> > -int ceph_osdc_copy_from(struct ceph_osd_client *osdc,
> > +struct ceph_osd_request *ceph_osdc_copy_from(
> > +                       struct ceph_osd_client *osdc,
> >                         u64 src_snapid, u64 src_version,
> >                         struct ceph_object_id *src_oid,
> >                         struct ceph_object_locator *src_oloc,
> > @@ -537,6 +538,8 @@ int ceph_osdc_copy_from(struct ceph_osd_client *osdc,
> >                         u32 truncate_seq, u64 truncate_size,
> >                         u8 copy_from_flags);
> >
> > +int ceph_osdc_wait_requests(struct list_head *osd_reqs);
> > +
> >  /* watch/notify */
> >  struct ceph_osd_linger_request *
> >  ceph_osdc_watch(struct ceph_osd_client *osdc,
> > diff --git a/net/ceph/osd_client.c b/net/ceph/osd_client.c
> > index b68b376d8c2f..c123e231eaf4 100644
> > --- a/net/ceph/osd_client.c
> > +++ b/net/ceph/osd_client.c
> > @@ -5346,23 +5346,47 @@ static int osd_req_op_copy_from_init(struct ceph_osd_request *req,
> >         return 0;
> >  }
> >
> > -int ceph_osdc_copy_from(struct ceph_osd_client *osdc,
> > -                       u64 src_snapid, u64 src_version,
> > -                       struct ceph_object_id *src_oid,
> > -                       struct ceph_object_locator *src_oloc,
> > -                       u32 src_fadvise_flags,
> > -                       struct ceph_object_id *dst_oid,
> > -                       struct ceph_object_locator *dst_oloc,
> > -                       u32 dst_fadvise_flags,
> > -                       u32 truncate_seq, u64 truncate_size,
> > -                       u8 copy_from_flags)
> > +int ceph_osdc_wait_requests(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_private_item);
> > +               list_del_init(&req->r_private_item);
> > +               err = ceph_osdc_wait_request(req->r_osdc, req);
> > +               if (err) {
> > +                       if (!ret)
> > +                               ret = err;
> > +                       dout("copy request failed (err=%d)\n", err);
> 
> This dout needs updating, but I'd just remove it.  The error code is
> there in other messages.
> 
> > +               }
> > +               ceph_osdc_put_request(req);
> > +       }
> > +
> > +       return ret;
> > +}
> > +EXPORT_SYMBOL(ceph_osdc_wait_requests);
> 
> Move this function after ceph_osdc_wait_request(), so that they are
> close to each other (and osd_req_op_copy_from_init() isn't separated
> from ceph_osdc_copy_from() by something unrelated).
> 
> Thanks,
> 
>                 Ilya