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btrfs-progs: fi defrag: change default extent target size to 32 MiB 

The kernel default is too low, 32 MiB is recommended and should give
better results.

Signed-off-by: David Sterba <dsterba@suse.com>
master
David Sterba 2016-07-28 13:14:08 +02:00
parent 2542112e0c
commit 2f732723d6
2 changed files with 21 additions and 6 deletions
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16
Documentation/btrfs-filesystem.asciidoc
View File

@ -117,15 +117,23 @@ compression. See also section 'EXAMPLES'.
-r::::
defragment files recursively in given directories
-f::::
flush data for each file before going to the next file. This will limit the amount
of dirty data to current file, otherwise the amount cumulates from several files
and may increase system load.
flush data for each file before going to the next file.
+
This will limit the amount of dirty data to current file, otherwise the amount
cumulates from several files and will increase system load. This can also lead
to ENOSPC if there's too much dirty data to write and it's not possible to make
the reservations for the new data (ie. how the COW design works).
+
-s <start>[kKmMgGtTpPeE]::::
defragmentation will start from the given offset, default is beginning of a file
-l <len>[kKmMgGtTpPeE]::::
defragment only up to 'len' bytes, default is the file size
-t <size>[kKmMgGtTpPeE]::::
target extent size, do not touch extents bigger than 'size'
target extent size, do not touch extents bigger than 'size', default: 32M
+
The value is only advisory and the final size of the extents may differ,
depending on the state of the free space and fragmentation or other internal
logic. Reasonable values are from tens to hundreds of megabytes.
*du* [options] <path> [<path>..]::
Calculate disk usage of the target files using FIEMAP. For individual

11
cmds-filesystem.c
View File

@ -968,7 +968,7 @@ static const char * const cmd_filesystem_defrag_usage[] = {
"-f flush data to disk immediately after defragmenting",
"-s start defragment only from byte onward",
"-l len defragment only up to len bytes",
"-t size target extent size hint",
"-t size target extent size hint (default: 32M)",
NULL
};
@ -1029,7 +1029,7 @@ static int cmd_filesystem_defrag(int argc, char **argv)
int flush = 0;
u64 start = 0;
u64 len = (u64)-1;
u64 thresh = 0;
u64 thresh;
int i;
int recursive = 0;
int ret = 0;
@ -1037,6 +1037,13 @@ static int cmd_filesystem_defrag(int argc, char **argv)
int compress_type = BTRFS_COMPRESS_NONE;
DIR *dirstream;
/*
* Kernel has a different default (256K) that is supposed to be safe,
* but it does not defragment very well. The 32M will likely lead to
* better results and is independent of the kernel default.
*/
thresh = 32 * 1024 * 1024;
defrag_global_errors = 0;
defrag_global_verbose = 0;
defrag_global_errors = 0;