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relay: Reduce streaming compression ratio from HIGH to LOW

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Fixes #40301

Signed-off-by: David Goulet <dgoulet@torproject.org>
This commit is contained in:
David Goulet 2021-02-18 12:49:33 -05:00
parent 26c2e843f9
commit d98c77b78e
5 changed files with 27 additions and 46 deletions
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4
changes/ticket40301 Normal file
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@ -0,0 +1,4 @@
o Minor bugfixes (relay):
- Reduce the compression level for data streaming from HIGH to LOW. Fixes
bug 40301; bugfix on 0.3.5.1-alpha.

35
src/feature/dircache/dircache.c
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@ -296,19 +296,22 @@ client_likes_consensus(const struct consensus_cache_entry_t *ent,
/** Return the compression level we should use for sending a compressed
* response of size <b>n_bytes</b>. */
STATIC compression_level_t
choose_compression_level(ssize_t n_bytes)
choose_compression_level(void)
{
if (! have_been_under_memory_pressure()) {
return HIGH_COMPRESSION; /* we have plenty of RAM. */
} else if (n_bytes < 0) {
return HIGH_COMPRESSION; /* unknown; might be big. */
} else if (n_bytes < 1024) {
/* This is the compression level choice for a stream.
*
* We always return LOW because this compression is done in the main thread
* thus we save CPU time as much as possible, and it is also done more than
* background compression for document we serve pre-compressed.
*
* GZip highest compression level (9) gives us a ratio of 49.72%
* Zstd lowest compression level (1) gives us a ratio of 47.38%
*
* Thus, as the network moves more and more to use Zstd when requesting
* directory documents that are not pre-cached, even at the
* lowest level, we still gain over GZip and thus help with load and CPU
* time on the network. */
return LOW_COMPRESSION;
} else if (n_bytes < 2048) {
return MEDIUM_COMPRESSION;
} else {
return HIGH_COMPRESSION;
}
}
/** Information passed to handle a GET request. */
@ -1078,7 +1081,7 @@ handle_get_status_vote(dir_connection_t *conn, const get_handler_args_t *args)
if (smartlist_len(items)) {
if (compress_method != NO_METHOD) {
conn->compress_state = tor_compress_new(1, compress_method,
choose_compression_level(estimated_len));
choose_compression_level());
}
SMARTLIST_FOREACH(items, const char *, c,
@ -1141,7 +1144,7 @@ handle_get_microdesc(dir_connection_t *conn, const get_handler_args_t *args)
if (compress_method != NO_METHOD)
conn->compress_state = tor_compress_new(1, compress_method,
choose_compression_level(size_guess));
choose_compression_level());
const int initial_flush_result = connection_dirserv_flushed_some(conn);
tor_assert_nonfatal(initial_flush_result == 0);
@ -1236,7 +1239,7 @@ handle_get_descriptor(dir_connection_t *conn, const get_handler_args_t *args)
write_http_response_header(conn, -1, compress_method, cache_lifetime);
if (compress_method != NO_METHOD)
conn->compress_state = tor_compress_new(1, compress_method,
choose_compression_level(size_guess));
choose_compression_level());
clear_spool = 0;
/* Prime the connection with some data. */
int initial_flush_result = connection_dirserv_flushed_some(conn);
@ -1332,7 +1335,7 @@ handle_get_keys(dir_connection_t *conn, const get_handler_args_t *args)
60*60);
if (compress_method != NO_METHOD) {
conn->compress_state = tor_compress_new(1, compress_method,
choose_compression_level(len));
choose_compression_level());
}
SMARTLIST_FOREACH(certs, authority_cert_t *, c,
@ -1484,7 +1487,7 @@ handle_get_next_bandwidth(dir_connection_t *conn,
compress_method, BANDWIDTH_CACHE_LIFETIME);
if (compress_method != NO_METHOD) {
conn->compress_state = tor_compress_new(1, compress_method,
choose_compression_level(len/2));
choose_compression_level());
log_debug(LD_DIR, "Compressing bandwidth file.");
} else {
log_debug(LD_DIR, "Not compressing bandwidth file.");

2
src/feature/dircache/dircache.h
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@ -26,7 +26,7 @@ MOCK_DECL(STATIC int, directory_handle_command_post,(dir_connection_t *conn,
STATIC int handle_post_hs_descriptor(const char *url, const char *body);
enum compression_level_t;
STATIC enum compression_level_t choose_compression_level(ssize_t n_bytes);
STATIC enum compression_level_t choose_compression_level(void);
struct get_handler_args_t;
STATIC int handle_get_hs_descriptor_v3(dir_connection_t *conn,

4
src/lib/compress/compress_zstd.c
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@ -49,8 +49,8 @@ memory_level(compression_level_t level)
default:
case BEST_COMPRESSION:
case HIGH_COMPRESSION: return 9;
case MEDIUM_COMPRESSION: return 8;
case LOW_COMPRESSION: return 7;
case MEDIUM_COMPRESSION: return 3;
case LOW_COMPRESSION: return 1;
}
}
#endif /* defined(HAVE_ZSTD) */

26
src/test/test_dir.c
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@ -5495,31 +5495,6 @@ dir_tests_directory_initiate_request(directory_request_t *req)
dir_tests_directory_initiate_request_called++;
}
static void
test_dir_choose_compression_level(void* data)
{
(void)data;
/* It starts under_memory_pressure */
tt_int_op(have_been_under_memory_pressure(), OP_EQ, 1);
tt_assert(HIGH_COMPRESSION == choose_compression_level(-1));
tt_assert(LOW_COMPRESSION == choose_compression_level(1024-1));
tt_assert(MEDIUM_COMPRESSION == choose_compression_level(2048-1));
tt_assert(HIGH_COMPRESSION == choose_compression_level(2048));
/* Reset under_memory_pressure timer */
cell_queues_check_size();
tt_int_op(have_been_under_memory_pressure(), OP_EQ, 0);
tt_assert(HIGH_COMPRESSION == choose_compression_level(-1));
tt_assert(HIGH_COMPRESSION == choose_compression_level(1024-1));
tt_assert(HIGH_COMPRESSION == choose_compression_level(2048-1));
tt_assert(HIGH_COMPRESSION == choose_compression_level(2048));
done: ;
}
/*
* Mock check_private_dir(), and always succeed - no need to actually
* look at or create anything on the filesystem.
@ -7325,7 +7300,6 @@ struct testcase_t dir_tests[] = {
DIR(should_not_init_request_to_ourselves, TT_FORK),
DIR(should_not_init_request_to_dir_auths_without_v3_info, 0),
DIR(should_init_request_to_dir_auths, 0),
DIR(choose_compression_level, 0),
DIR(dump_unparseable_descriptors, 0),
DIR(populate_dump_desc_fifo, 0),
DIR(populate_dump_desc_fifo_2, 0),