Add support for runtime log compression

[fio.git] / HOWTO

diff --git a/HOWTO b/HOWTO
index 3001fe74a0b6cffe19fba612e95c082580085c01..e94d09f334d66fa58fe4cd76391a8f6e7f03e382 100644 (file)
--- a/HOWTO
+++ b/HOWTO
@@ -1336,6 +1336,20 @@ log_avg_msec=int By default, fio will log an entry in the iops, latency,
 log_offset=int If this is set, the iolog options will include the byte
                offset for the IO entry as well as the other data values.
 
+log_compression=int    If this is set, fio will compress the IO logs as
+               it goes, to keep the memory footprint lower. When a log
+               reaches the specified size, that chunk is removed and
+               compressed in the background. Given that IO logs are
+               fairly highly compressible, this yields a nice memory
+               savings for longer runs. The downside is that the
+               compression will consume some background CPU cycles, so
+               it may impact the run. This, however, is also true if
+               the logging ends up consuming most of the system memory.
+               So pick your poison. The IO logs are saved normally at the
+               end of a run, by decompressing the chunks and storing them
+               in the specified log file. This feature depends on the
+               availability of zlib.
+
 lockmem=int    Pin down the specified amount of memory with mlock(2). Can
                potentially be used instead of removing memory or booting
                with less memory to simulate a smaller amount of memory.