nbdkit/0006-cache-cow-Use-a-64K-block-size-by-default.patch

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From e0f76fe019449c81297de39ddd6a12006d94481a Mon Sep 17 00:00:00 2001
From: "Richard W.M. Jones" <rjones@redhat.com>
Date: Mon, 26 Jul 2021 17:39:23 +0100
Subject: [PATCH] cache, cow: Use a 64K block size by default
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.
(cherry picked from commit c1905b0a28677d961babdb16d6f30ae61042c825)
---
filters/cache/cache.c | 2 +-
filters/cache/nbdkit-cache-filter.pod | 4 ++--
filters/cow/blk.h | 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/cache.c b/filters/cache/cache.c
index 109ac89e..c912c5fb 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/filters/cache/nbdkit-cache-filter.pod b/filters/cache/nbdkit-cache-filter.pod
index 6cbd1c08..df9c1f99 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/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
--
2.31.1