Update compression documentation

Make it clearer (hopefully) that buffer_compress_chunk should be
used if the user wants a finer granularity than the write block
size.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/HOWTO b/HOWTO
index f151350ce39b221246316848c4648b80b7a9b1c0..e510e18c4c782a3335f6edaf29fed89799b9445c 100644 (file)
--- a/HOWTO
+++ b/HOWTO
@@ -1453,8 +1453,8 @@ Buffers and memory
        mix of random data and a fixed pattern. The fixed pattern is either zeros,
        or the pattern specified by :option:`buffer_pattern`. If the pattern option
        is used, it might skew the compression ratio slightly. Note that this is per
-       block size unit, for file/disk wide compression level that matches this
-       setting, you'll also want to set :option:`refill_buffers`.
+       block size unit, see :option:`buffer_compress_chunk` for setting a finer
+       granularity of compression regions.
 
 .. option:: buffer_compress_chunk=int
 
@@ -1463,7 +1463,8 @@ Buffers and memory
        will provide :option:`buffer_compress_percentage` of blocksize random data,
        followed by the remaining zeroed. With this set to some chunk size smaller
        than the block size, fio can alternate random and zeroed data throughout the
-       I/O buffer.
+       I/O buffer. This is particularly useful when bigger block sizes are used
+       for a job.
 
 .. option:: buffer_pattern=str
 

diff --git a/fio.1 b/fio.1
index 198b9d85f872a4b959fd997dca43326a9f5b5ff4..8e983724253e3738e1206d624adaf93c2a9294bd 100644 (file)
--- a/fio.1
+++ b/fio.1
@@ -1242,8 +1242,8 @@ WRITEs) that compresses to the specified level. Fio does this by providing a
 mix of random data and a fixed pattern. The fixed pattern is either zeros,
 or the pattern specified by \fBbuffer_pattern\fR. If the pattern option
 is used, it might skew the compression ratio slightly. Note that this is per
-block size unit, for file/disk wide compression level that matches this
-setting, you'll also want to set \fBrefill_buffers\fR.
+block size unit, see \fBbuffer_compress_chunk\fR for setting a finer granularity
+of compressible regions.
 .TP
 .BI buffer_compress_chunk \fR=\fPint
 See \fBbuffer_compress_percentage\fR. This setting allows fio to manage
@@ -1251,7 +1251,8 @@ how big the ranges of random data and zeroed data is. Without this set, fio
 will provide \fBbuffer_compress_percentage\fR of blocksize random data,
 followed by the remaining zeroed. With this set to some chunk size smaller
 than the block size, fio can alternate random and zeroed data throughout the
-I/O buffer.
+I/O buffer. This is particularly useful when bigger block sizes are used
+for a job.
 .TP
 .BI buffer_pattern \fR=\fPstr
 If set, fio will fill the I/O buffers with this pattern or with the contents