[Libguestfs] [PATCH nbdkit 7/7] cache, cow: Use a 64K block size by default

[Richard W.M. Jones]

Based on the results presented in the previous commit, use a 64K block
size by default in both the cache and cow filters.  For the cache
filter you could go back to a 4K block size if you wanted by using the
cache-min-block-size=4K parameter.  For cow it is compiled in so
cannot be adjusted.
---
 filters/cache/nbdkit-cache-filter.pod |  4 ++--
 filters/cow/blk.h                     |  2 +-
 filters/cache/cache.c                 |  2 +-
 tests/test-cache-block-size.sh        |  2 +-
 tests/test-cow-extents1.sh            | 33 +++++++++++++++------------
 5 files changed, 23 insertions(+), 20 deletions(-)

diff --git a/filters/cache/nbdkit-cache-filter.pod b/filters/cache/nbdkit-cache-filter.pod
index 9511e91b..99707373 100644
--- a/filters/cache/nbdkit-cache-filter.pod
+++ b/filters/cache/nbdkit-cache-filter.pod
@@ -65,8 +65,8 @@ or can cheaply reconstruct.
 Set the minimum block size used by the cache.  This must be a power of
 2 and E<ge> 4096.
 
-The default is 4096, or the block size of the filesystem which
-contains the temporary file storing the cache (whichever is larger).
+The default is 64K, or the block size of the filesystem which contains
+the temporary file storing the cache (whichever is larger).
 
 =item B<cache-max-size=>SIZE
 
diff --git a/filters/cow/blk.h b/filters/cow/blk.h
index b066c602..1bc85283 100644
--- a/filters/cow/blk.h
+++ b/filters/cow/blk.h
@@ -36,7 +36,7 @@
 /* Size of a block in the overlay.  A 4K block size means that we need
  * 64 MB of memory to store the bitmap for a 1 TB underlying image.
  */
-#define BLKSIZE 4096
+#define BLKSIZE 65536
 
 /* Initialize the overlay and bitmap. */
 extern int blk_init (void);
diff --git a/filters/cache/cache.c b/filters/cache/cache.c
index 48a20c3b..f7b01039 100644
--- a/filters/cache/cache.c
+++ b/filters/cache/cache.c
@@ -73,7 +73,7 @@
 static pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
 
 unsigned blksize;            /* actual block size (picked by blk.c) */
-unsigned min_block_size = 4096;
+unsigned min_block_size = 65536;
 enum cache_mode cache_mode = CACHE_MODE_WRITEBACK;
 int64_t max_size = -1;
 unsigned hi_thresh = 95, lo_thresh = 80;
diff --git a/tests/test-cache-block-size.sh b/tests/test-cache-block-size.sh
index a2a27407..d20cc940 100755
--- a/tests/test-cache-block-size.sh
+++ b/tests/test-cache-block-size.sh
@@ -47,7 +47,7 @@ truncate -s 128K cache-block-size.img
 
 # Run nbdkit with the caching filter.
 start_nbdkit -P cache-block-size.pid -U $sock --filter=cache \
-             file cache-block-size.img cache-min-block-size=64K
+             file cache-block-size.img cache-min-block-size=4K
 
 nbdsh --connect "nbd+unix://?socket=$sock" \
       -c '
diff --git a/tests/test-cow-extents1.sh b/tests/test-cow-extents1.sh
index 8e0e0383..ebfd83f6 100755
--- a/tests/test-cow-extents1.sh
+++ b/tests/test-cow-extents1.sh
@@ -65,7 +65,7 @@ cleanup_fn rm -f $files
 
 # Create a base file which is half allocated, half sparse.
 dd if=/dev/urandom of=$base count=128 bs=1K
-truncate -s 256K $base
+truncate -s 4M $base
 lastmod="$(stat -c "%y" $base)"
 
 # Run nbdkit with a COW overlay.
@@ -76,30 +76,33 @@ uri="nbd+unix:///?socket=$sock"
 nbdinfo --map "$uri" > $out
 cat $out
 if [ "$(tr -s ' ' < $out | cut -d' ' -f 1-4)" != " 0 131072 0
- 131072 131072 3" ]; then
+ 131072 4063232 3" ]; then
     echo "$0: unexpected initial file map"
     exit 1
 fi
 
 # Punch some holes.
 nbdsh -u "$uri" \
-      -c 'h.trim(4096, 4096)' \
-      -c 'h.trim(4098, 16383)' \
-      -c 'h.pwrite(b"1"*4096, 65536)' \
-      -c 'h.trim(8192, 131072)' \
-      -c 'h.pwrite(b"2"*8192, 196608)'
+      -c 'bs = 65536' \
+      -c 'h.trim(bs, bs)' \
+      -c 'h.trim(bs+2, 4*bs-1)' \
+      -c 'h.pwrite(b"1"*bs, 16*bs)' \
+      -c 'h.trim(2*bs, 32*bs)' \
+      -c 'h.pwrite(b"2"*(2*bs), 48*bs)'
 
 # The extents map should be fully allocated.
 nbdinfo --map "$uri" > $out
 cat $out
-if [ "$(tr -s ' ' < $out | cut -d' ' -f 1-4)" != " 0 4096 0
- 4096 4096 3
- 8192 8192 0
- 16384 4096 3
- 20480 110592 0
- 131072 65536 3
- 196608 8192 0
- 204800 57344 3" ]; then
+if [ "$(tr -s ' ' < $out | cut -d' ' -f 1-4)" != " 0 65536 0
+ 65536 131072 3
+ 196608 65536 0
+ 262144 65536 3
+ 327680 65536 0
+ 393216 655360 3
+ 1048576 65536 0
+ 1114112 2031616 3
+ 3145728 131072 0
+ 3276800 917504 3" ]; then
     echo "$0: unexpected trimmed file map"
     exit 1
 fi
-- 
2.32.0