Re: [PATCH v3 1/1] ceph: parallelize all copy-from requests in copy_file_range

[Luis Henriques]

On Tue, Feb 04, 2020 at 08:30:03AM -0500, Jeff Layton wrote:
> On Mon, 2020-02-03 at 16:51 +0000, Luis Henriques 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.
> > 
> 
> Looks good overall. A few nits below:
> 
> > Signed-off-by: Luis Henriques <lhenriques@xxxxxxxx>
> > ---
> >  fs/ceph/file.c                  | 45 +++++++++++++++++++++-----
> >  include/linux/ceph/osd_client.h |  6 +++-
> >  net/ceph/osd_client.c           | 56 +++++++++++++++++++++++++--------
> >  3 files changed, 85 insertions(+), 22 deletions(-)
> > 
> > diff --git a/fs/ceph/file.c b/fs/ceph/file.c
> > index 1e6cdf2dfe90..b9d8ffafb8c5 100644
> > --- a/fs/ceph/file.c
> > +++ b/fs/ceph/file.c
> > @@ -1943,12 +1943,15 @@ 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;
> > +	unsigned int max_copies, copy_count, reqs_complete = 0;
> >  	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 +2086,13 @@ 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: max_copies holds the number of allowed
> > +	 * in-flight 'copy-from' requests before waiting for their completion
> > +	 */
> > +	max_copies = (src_fsc->mount_options->wsize / object_size) * 4;
> 
> A note about why you chose to multiply by a factor of 4 here would be
> good. In another year or two, we won't remember.

Sure, but to be honest I just picked an early suggestion from Ilya :-)
In practice it means that, by default, 64 will be the maximum requests
in-flight.  I tested this value, and it looked OK although in the (very
humble) test cluster I've used a value of 16 (i.e. dropping the factor of
4) wasn't much worst.

> > +	copy_count = max_copies;
> >  	while (len >= object_size) {
> >  		ceph_calc_file_object_mapping(&src_ci->i_layout, src_off,
> >  					      object_size, &src_objnum,
> > @@ -2097,7 +2107,7 @@ 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,
> > @@ -2108,21 +2118,40 @@ 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 (err == -EOPNOTSUPP) {
> > -				src_fsc->have_copy_from2 = false;
> > -				pr_notice("OSDs don't support 'copy-from2'; "
> > -					  "disabling copy_file_range\n");
> > -			}
> > +		if (IS_ERR(req)) {
> > +			err = PTR_ERR(req);
> >  			dout("ceph_osdc_copy_from returned %d\n", err);
> > +
> > +			/* wait for all queued requests */
> > +			ceph_osdc_wait_requests(&osd_reqs, &reqs_complete);
> > +			ret += reqs_complete * object_size; /* Update copied bytes */
> >  			if (!ret)
> >  				ret = err;
> >  			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;
> > +		/*
> > +		 * Wait requests if we've reached the maximum requests allowed
> 
> "Wait for requests..."
> 
> > +		 * or if this was the last copy
> > +		 */
> > +		if ((--copy_count == 0) || (len < object_size)) {
> > +			err = ceph_osdc_wait_requests(&osd_reqs, &reqs_complete);
> > +			ret += reqs_complete * object_size; /* Update copied bytes */
> > +			if (err) {
> > +				if (err == -EOPNOTSUPP) {
> > +					src_fsc->have_copy_from2 = false;
> > +					pr_notice("OSDs don't support 'copy-from2'; "
> > +						  "disabling copy_file_range\n");
> > +				}
> > +				if (!ret)
> > +					ret = err;
> > +				goto out_caps;
> > +			}
> > +			copy_count = max_copies;
> > +		}
> >  	}
> >  
> >  	if (len)
> > diff --git a/include/linux/ceph/osd_client.h b/include/linux/ceph/osd_client.h
> > index 5a62dbd3f4c2..0121767cd65e 100644
> > --- a/include/linux/ceph/osd_client.h
> > +++ b/include/linux/ceph/osd_client.h
> > @@ -496,6 +496,9 @@ extern int ceph_osdc_start_request(struct ceph_osd_client *osdc,
> >  extern void ceph_osdc_cancel_request(struct ceph_osd_request *req);
> >  extern int ceph_osdc_wait_request(struct ceph_osd_client *osdc,
> >  				  struct ceph_osd_request *req);
> > +extern int ceph_osdc_wait_requests(struct list_head *osd_reqs,
> > +				   unsigned int *reqs_complete);
> > +
> >  extern void ceph_osdc_sync(struct ceph_osd_client *osdc);
> >  
> >  extern void ceph_osdc_flush_notifies(struct ceph_osd_client *osdc);
> > @@ -526,7 +529,8 @@ 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,
> > diff --git a/net/ceph/osd_client.c b/net/ceph/osd_client.c
> > index b68b376d8c2f..df9f342f860a 100644
> > --- a/net/ceph/osd_client.c
> > +++ b/net/ceph/osd_client.c
> > @@ -4531,6 +4531,35 @@ int ceph_osdc_wait_request(struct ceph_osd_client *osdc,
> >  }
> >  EXPORT_SYMBOL(ceph_osdc_wait_request);
> >  
> > +/*
> > + * wait for all requests to complete in list @osd_reqs, returning the number of
> > + * successful completions in @reqs_complete
> > + */
> 
> Maybe consider just having it return a positive reqs_complete value or a
> negative error code, and drop the reqs_complete pointer argument? It'd
> also be good to note what this function returns.

In my (flawed) design I wanted to know that there was an error in a
request but also how many successful requests.  But after the last review
from Ilya I'll probably need to revisit this anyway.

> > +int ceph_osdc_wait_requests(struct list_head *osd_reqs,
> > +			    unsigned int *reqs_complete)
> > +{
> > +	struct ceph_osd_request *req;
> > +	int ret = 0, err;
> > +	unsigned int counter = 0;
> > +
> > +	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);
> 
> ceph_osdc_wait_request calls wait_request_timeout, which uses a killable
> sleep. That's better than uninterruptible sleep, but maybe it'd be good
> to use an interruptible sleep here instead? Having to send fatal signals
> when things are stuck kind of sucks.

Good point.  It looks like Zheng changed this to a killable sleep in
commit 0e76abf21e76 ("libceph: make ceph_osdc_wait_request()
uninterruptible").  I guess you're suggesting to add a new function
(wait_request_uninterruptible_timeout) that would be used only here,
right?

Cheers,
--
Luís