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mirror: Remove server I/O lock and dirty map

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Given our bitset_stream events, we no longer need to worry about
keeping track of the dirty map. This also lets us rip out the
server I/O lock from mirroring.

It's possible that we can remove the lock from client.c as well at
this point, but I need to have a bit more of a think about possible
races
This commit is contained in:
nick
2013-09-19 15:18:30 +01:00
parent a5c296f948
commit eb80c0d235
5 changed files with 109 additions and 130 deletions
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4
src/client.c
View File

@@ -138,7 +138,6 @@ void write_not_zeroes(struct client* client, uint64_t from, uint64_t len)
* are interested in that fact.
*/
bitset_set_range( map, from, run );
server_dirty(client->serve, from, run);
len -= run;
from += run;
}
@@ -165,7 +164,6 @@ void write_not_zeroes(struct client* client, uint64_t from, uint64_t len)
if ( !all_zeros ) {
memcpy(client->mapped+from, zerobuffer, blockrun);
bitset_set_range(map, from, blockrun);
server_dirty(client->serve, from, blockrun);
/* at this point we could choose to
* short-cut the rest of the write for
* faster I/O but by continuing to do it
@@ -467,8 +465,6 @@ void client_reply_to_write( struct client* client, struct nbd_request request )
request.len
);
/* Ensure this updated block is written in the event of a mirror op */
server_dirty(client->serve, request.from, request.len);
/* the allocation_map is shared between client threads, and may be
* being built. We need to reflect the write in it, as it may be in
* a position the builder has already gone over.

212
src/mirror.c
View File

@@ -76,8 +76,17 @@ struct mirror_ctrl {
ev_timer limit_watcher;
ev_io abandon_watcher;
/* We set this if the bitset stream is getting uncomfortably full, and unset
* once it's emptier */
int clear_events;
/* This is set once all clients have been closed, to let the mirror know
* it's safe to finish once the queue is empty */
int last_pass;
/* Use this to keep track of what we're copying at any moment */
struct xfer xfer;
};
struct mirror * mirror_alloc(
@@ -149,8 +158,6 @@ void mirror_init( struct mirror * mirror, const char * filename )
madvise( mirror->mapped, size, MADV_SEQUENTIAL ),
SHOW_ERRNO( "Failed to madvise() %s", filename )
);
mirror->dirty_map = bitset_alloc(size, 4096);
}
@@ -158,18 +165,15 @@ void mirror_init( struct mirror * mirror, const char * filename )
void mirror_reset( struct mirror * mirror )
{
NULLCHECK( mirror );
NULLCHECK( mirror->dirty_map );
mirror_set_state( mirror, MS_INIT );
/* See the caveats in mirror_run if you change this! */
bitset_set(mirror->dirty_map);
mirror->all_dirty = 0;
mirror->all_clean = 0;
mirror->pass = 0;
mirror->this_pass_dirty = 0;
mirror->this_pass_clean = 0;
mirror->migration_started = 0;
mirror->pass_offset = 0;
return;
}
@@ -206,7 +210,6 @@ void mirror_destroy( struct mirror *mirror )
self_pipe_destroy( mirror->abandon_signal );
free(mirror->connect_to);
free(mirror->connect_from);
bitset_free( mirror->dirty_map );
free(mirror);
}
@@ -226,13 +229,16 @@ static const int mirror_maximum_passes = 7;
#define mirror_last_pass (mirror_maximum_passes - 1)
/* THIS FUNCTION MUST ONLY BE CALLED WITH THE SERVER'S IO LOCKED. */
/* This must not be called if there's any chance of further I/O. Methods to
* ensure this include:
* - call server_lock_io()
* - call server_forbid_new_clients() followed by a successful server_close_clients() ; server_join_clients()
*/
void mirror_on_exit( struct server * serve )
{
/* If we're still here, we can shut the server down.
*
* It doesn't matter if we get new client connections before
* now, the IO lock will stop them from doing anything.
*
*/
debug("serve_signal_close");
serve_signal_close( serve );
@@ -346,46 +352,61 @@ int mirror_should_quit( struct mirror * mirror )
}
}
/* Iterates through the bitmap, finding a dirty run to form the basis of the
/*
* If there's an event in the bitset stream of the serve allocation map, we
* use it to construct the next transfer request, covering precisely the area
* that has changed. If there are no events, we take the next
* TODO: should we detect short events and lengthen them to reduce overhead?
*
* iterates through the bitmap, finding a dirty run to form the basis of the
* next transfer, then puts it together. */
int mirror_setup_next_xfer( struct mirror_ctrl *ctrl )
{
struct mirror* mirror = ctrl->mirror;
uint64_t current, run, size = ctrl->serve->size;
int found = 0;
struct server* serve = ctrl->serve;
struct bitset_stream_entry e = { .event = BITSET_STREAM_UNSET };
uint64_t current = mirror->pass_offset, run = 0, size = serve->size;
do {
int run_is_set = 0;
current = mirror->this_pass_dirty + mirror->this_pass_clean;
/* Technically, we'd be interested in UNSET events too, but they are never
* generated. TODO if that changes.
*
* We use ctrl->clear_events to start emptying the stream when it's half
* full, and stop when it's a quarter full. This stops a busy client from
* stalling a migration forever. FIXME: made-up numbers.
*/
if ( bitset_stream_size( serve->allocation_map ) > BITSET_STREAM_SIZE / 2 ) {
ctrl->clear_events = 1;
}
run = bitset_run_count_ex(
mirror->dirty_map, current, mirror_longest_write, &run_is_set
);
while ( ( ctrl->last_pass || ctrl->clear_events ) && e.event != BITSET_STREAM_SET ) {
debug("Dequeueing event");
bitset_stream_dequeue( ctrl->serve->allocation_map, &e );
debug("Dequeued event %i, %zu, %zu", e.event, e.from, e.len);
if ( current + run > size ) {
debug(
"Size not divisible by %i, adjusting final block",
block_allocation_resolution
);
if ( bitset_stream_size( serve->allocation_map ) < BITSET_STREAM_SIZE / 4 ) {
ctrl->clear_events = 0;
}
}
if ( e.event == BITSET_STREAM_SET ) {
current = e.from;
run = e.len;
} else if ( !ctrl->last_pass && current < serve->size ) {
current = mirror->pass_offset;
run = mirror_longest_write;
/* Adjust final block if necessary */
if ( current + run > serve->size ) {
run = size - current;
}
/* FIXME: we could avoid sending sparse areas of the disc here, and
* probably save a lot of bandwidth and time (if we know the destination
* starts off zeroed). */
if ( run_is_set ) {
found = 1;
} else {
mirror->this_pass_clean += run;
mirror->all_clean += run;
mirror->pass_offset += run;
}
} while ( !found && current + run < size );
/* current and run specify our next transfer */
if ( !found ) {
if ( run == 0 ) {
return 0;
}
debug( "Next dirty block: current=%"PRIu64", run=%"PRIu64, current, run );
debug( "Next transfer: current=%"PRIu64", run=%"PRIu64, current, run );
struct nbd_request req = {
.magic = REQUEST_MAGIC,
.type = REQUEST_WRITE,
@@ -418,7 +439,7 @@ int mirror_exceeds_max_bps( struct mirror *mirror )
return 0;
}
// ONLY CALL THIS WHEN SERVER IO IS LOCKED
// ONLY CALL THIS AFTER CLOSING CLIENTS
void mirror_complete( struct server *serve )
{
/* FIXME: Pretty sure this is broken, if action != !QUIT. Just moving code
@@ -459,17 +480,6 @@ static void mirror_write_cb( struct ev_loop *loop, ev_io *w, int revents )
} else {
data_loc = ctrl->mirror->mapped + xfer->from + ( xfer->written - hdr_size );
to_write = xfer->len - ( ctrl->xfer.written - hdr_size );
// If we're in the last pass, we'll be locked anyway. If we're not in
// the last pass, we want to be locked for every write() call that
// we issue, to avoid the blocks being updated while we work. In
// particular, bitset_run_clear() must be called while the I/O is locked
// or we might clear a bit that had been set by another write.
if ( !server_io_locked( ctrl->serve ) ) {
server_lock_io( ctrl->serve );
debug( "In lock block" );
}
}
// Actually read some bytes
@@ -484,24 +494,11 @@ static void mirror_write_cb( struct ev_loop *loop, ev_io *w, int revents )
debug( "to_write was %"PRIu64", xfer->written was %"PRIu64, to_write, xfer->written );
ctrl->xfer.written += count;
// We write some bytes, so reset the timer
// We wrote some bytes, so reset the timer
ev_timer_again( ctrl->ev_loop, &ctrl->timeout_watcher );
// All bytes written, so now we need to read the NBD reply back.
if ( ctrl->xfer.written == ctrl->xfer.len + hdr_size ) {
// We can, however, clear the run here. If it turns out that the
// NBD request has been rejected, we're discarding it anyway, so the
// wrong data won't get used. If the request is a success, any blocks
// written to while waiting for the reply will be copied in the next
// pass; if it's the final pass, I/O remains locked.
debug( "Clearing bitset from=%"PRIu64" run=%"PRIu64", ctr->xfer.from, ctrl->xfer.len" );
bitset_clear_range( ctrl->mirror->dirty_map, ctrl->xfer.from, ctrl->xfer.len );
if ( ctrl->mirror->pass != mirror_last_pass ) {
debug( "Leaving lock block" );
server_unlock_io( ctrl->serve );
}
ev_io_start( loop, &ctrl->read_watcher );
ev_io_stop( loop, &ctrl->write_watcher );
}
@@ -591,55 +588,51 @@ static void mirror_read_cb( struct ev_loop *loop, ev_io *w, int revents )
/* This next bit could take a little while, which is fine */
ev_timer_stop( ctrl->ev_loop, &ctrl->timeout_watcher );
do {
// This pass complete
if ( m->this_pass_dirty + m->this_pass_clean == ctrl->serve->size ) {
debug( "Pass %d completed", m->pass );
/* Set up the next transfer, which may be n+1 in the current pass,
* or 0 in a new pass. If we can't find another transfer to do, that
* means the pass is complete. Advance pass and re-run the end-of-
* pass logic to complete migration ( pass == mirror_last_pass ), or
* move onto the last pass ( pass < mirror_last_pass, by virtue of
* this_pass_dirty being 0 ).
*/
int finished_setup = 0;
// last pass completed
if ( m->pass >= mirror_last_pass ) {
/* This was the last pass, so finish. */
/* Set up the next transfer, which may be pass_offset + mirror_longest_write
* or an event from the bitset stream. When pass_offset hits serve->size,
* we disable new clients from connecting, disconnect existing clients, and
* wait for the bitset stream to empty. At that point, we know that source
* and destination have the same data, so can finish.
*/
do {
if ( m->pass_offset == ctrl->serve->size ) {
debug( "Pass %d completed", m->pass );
if ( ctrl->last_pass ) {
mirror_complete( ctrl->serve );
ev_break( loop, EVBREAK_ONE );
return;
}
// this was not the last pass - set up for the next run.
if ( m->this_pass_dirty < mirror_last_pass_after_bytes_written ) {
/* Quiet disc, so skip to the final pass */
m->pass = mirror_last_pass;
} else {
m->pass++;
}
// FIXME: Can status race with us if it inspects state here?
m->this_pass_dirty = 0;
m->this_pass_clean = 0;
ctrl->last_pass++;
m->pass++; // TODO: remove this in favour of last_pass?
debug( "mirror start pass=%d", m->pass );
if ( m->pass == mirror_last_pass ) {
/* This is the start of our next pass. If it happens to be the
* final pass, we need to wait for all the clients to exit before
* continuing */
debug( "In lock block for last pass" );
/* FIXME: this could block */
/* Prevent further I/O from happening.
* FIXME: We should actually only do this if the amount of data
* left to transfer is under a certain threshold. As-is, we have
* no control over length of I/O freeze - it's entirely
* dependent on amount of traffic from the guest. More traffic =
* longer downtime.
*/
server_forbid_new_clients( ctrl->serve );
server_close_clients( ctrl->serve );
server_join_clients( ctrl->serve );
}
// FIXME: In theory, we won't need this any more...
server_lock_io( ctrl->serve );
} else {
/* Use mirror_setup_next_xfer to find out what to read next */
finished_setup = mirror_setup_next_xfer( ctrl );
}
}
} while ( !mirror_setup_next_xfer( ctrl ) );
} while ( !finished_setup );
ev_io_stop( loop, &ctrl->read_watcher );
/* FIXME: Should we ignore the bwlimit after server_close_clients has been called? */
if ( mirror_exceeds_max_bps( m ) ) {
/* We're over the bandwidth limit, so don't move onto the next transfer
* yet. Our limit_watcher will move us on once we're OK. timeout_watcher
@@ -719,17 +712,13 @@ void mirror_run( struct server *serve )
info("Starting mirror" );
/* mirror_setup_next_xfer won't be able to cope with this, so special-case
* it here.
* TODO: Another case we won't be able to handle is a non-zero-sized image
* where none of the blocks are set in the first pass. As it happens, we
* start with all blocks set and then pare them down, so it doesn't happen
* in the current codebase - but watch out for the future!
* it here. There can't be any writes going on, so don't bother locking
* anything.
*
*/
if ( serve->size == 0 ) {
info( "0-byte image special case" );
server_lock_io( serve );
mirror_complete( serve );
server_unlock_io( serve );
return;
}
@@ -739,7 +728,6 @@ void mirror_run( struct server *serve )
ctrl.serve = serve;
ctrl.mirror = m;
ctrl.ev_loop = EV_DEFAULT;
/* gcc warns on -O2. clang is fine. Seems to be the fault of ev.h */
@@ -776,21 +764,21 @@ void mirror_run( struct server *serve )
* can handle rate-limiting and weird error conditions better. TODO: We
* should expand the event loop upwards so we can do the same there too */
sock_set_nonblock( m->client, 1 );
bitset_stream_on( serve->allocation_map );
info( "Entering event loop" );
ev_run( ctrl.ev_loop, 0 );
info( "Exited event loop" );
/* Parent code might expect a non-blocking socket */
sock_set_nonblock( m->client, 0 );
/* Errors in the event loop don't track I/O lock state or try to restore
* it to something sane - they just terminate the event loop with state !=
* MS_DONE. We unlock I/O and re-allow new clients here if necessary.
* MS_DONE. We re-allow new clients here if necessary.
*/
if ( server_io_locked( serve ) ) {
server_unlock_io( serve );
}
if ( m->action_at_finish == ACTION_NOTHING || m->commit_state != MS_DONE ) {
server_allow_new_clients( serve );
}
@@ -800,6 +788,11 @@ void mirror_run( struct server *serve )
if ( m->commit_state != MS_DONE ) {
error( "Event loop exited, but mirroring is not complete" );
/* mirror_reset will be called before a retry, so keeping hold of events
* between now and our next mirroring attempt is not useful
*/
bitset_stream_off( serve->allocation_map );
}
return;
@@ -845,7 +838,6 @@ void* mirror_runner(void* serve_params_uncast)
NULLCHECK( serve );
NULLCHECK( serve->mirror );
struct mirror * mirror = serve->mirror;
NULLCHECK( mirror->dirty_map );
error_set_handler( (cleanup_handler *) mirror_cleanup, serve );

4
src/mirror.h
View File

@@ -78,7 +78,9 @@ struct mirror {
enum mirror_finish_action action_at_finish;
char *mapped;
struct bitset_mapping *dirty_map;
/* Keep an eye on where in the current pass we are */
uint64_t pass_offset;
enum mirror_state commit_state;

10
src/serve.c
View File

@@ -119,16 +119,6 @@ void server_unlink( struct server * serve )
}
void server_dirty(struct server *serve, off64_t from, int len)
{
NULLCHECK( serve );
if (serve->mirror) {
bitset_set_range(serve->mirror->dirty_map, from, len);
}
}
#define SERVER_LOCK( s, f, msg ) \
do { NULLCHECK( s ); \
FATAL_IF( 0 != flexthread_mutex_lock( s->f ), msg ); } while (0)

1
src/serve.h
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@@ -117,7 +117,6 @@ struct server * server_create(
int success );
void server_destroy( struct server * );
int server_is_closed(struct server* serve);
void server_dirty(struct server *serve, off64_t from, int len);
void server_lock_io( struct server * serve);
void server_unlock_io( struct server* serve );
void serve_signal_close( struct server *serve );