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add nullrw feature to facilitate benchmarking

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Antonio SJ Musumeci 2017-05-26 16:51:30 -04:00
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commit 87c2f2f9dc
12 changed files with 164 additions and 12 deletions
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34
README.md
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@ -1,6 +1,6 @@
% mergerfs(1) mergerfs user manual
% Antonio SJ Musumeci <trapexit@spawn.link>
% 2017-02-18
% 2017-05-26
# NAME
@ -40,6 +40,7 @@ mergerfs -o&lt;options&gt; &lt;srcmounts&gt; &lt;mountpoint&gt;
* **dropcacheonclose**: when a file is requested to be closed call `posix_fadvise` on it first to instruct the kernel that we no longer need the data and it can drop its cache. Recommended when **direct_io** is not enabled to limit double caching. (default: false)
* **symlinkify**: when enabled (set to **true**) and a file is not writable and its mtime or ctime is older than **symlinkify_timeout** files will be reported as symlinks to the original files. Please read more below before using. (default: false)
* **symlinkify_timeout**: time to wait, in seconds, to activate the **symlinkify** behavior. (default: 3600)
* **nullrw**: turns reads and writes into no-ops. The request will succeed but do nothing. Useful for benchmarking mergerfs. (default: false)
* **fsname**: sets the name of the filesystem as seen in **mount**, **df**, etc. Defaults to a list of the source paths concatenated together with the longest common prefix removed.
* **func.&lt;func&gt;=&lt;policy&gt;**: sets the specific FUSE function's policy. See below for the list of value types. Example: **func.getattr=newest**
* **category.&lt;category&gt;=&lt;policy&gt;**: Sets policy of all FUSE functions in the provided category. Example: **category.create=mfs**
@ -77,6 +78,37 @@ Due to the levels of indirection introduced by mergerfs and the underlying techn
**WARNING:** Some backup solutions, such as CrashPlan, do not backup the target of a symlink. If using this feature it will be necessary to point any backup software to the original drives or configure the software to follow symlinks if such an option is available. Alternatively create two mounts. One for backup and one for general consumption.
### nullrw
Due to how FUSE works there is an overhead to all requests made to a FUSE filesystem. Meaning that even a simple passthrough will have some slowdown. However, generally the overhead is minimal in comparison to the cost of the underlying I/O. By disabling the underlying I/O we can test the theoretical performance boundries.
By enabling `nullrw` mergerfs will work as it always does **except** that all reads and writes will be no-ops. A write will succeed (the size of the write will be returned as if it were successful) but mergerfs does nothing with the data it was given. Similarly a read will return the size requested but won't touch the buffer.
Example:
```
$ dd if=/dev/zero of=/path/to/mergerfs/mount/benchmark ibs=1M obs=512 count=1024
1024+0 records in
2097152+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 15.4067 s, 69.7 MB/s
$ dd if=/dev/zero of=/path/to/mergerfs/mount/benchmark ibs=1M obs=1M count=1024
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 0.219585 s, 4.9 GB/s
$ dd if=/path/to/mergerfs/mount/benchmark of=/dev/null bs=512 count=102400
102400+0 records in
102400+0 records out
52428800 bytes (52 MB, 50 MiB) copied, 0.757991 s, 69.2 MB/s
$ dd if=/path/to/mergerfs/mount/benchmark of=/dev/null bs=1M count=1024
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 0.18405 s, 5.8 GB/s
```
It's important to test with different `obs` (output block size) values since the relative overhead is greater with smaller values. As you can see above the size of a read or write can massively impact theoretical performance. If an application performs much worse through mergerfs it could very well be that it doesn't optimally size its read and write requests.
# FUNCTIONS / POLICIES / CATEGORIES
The POSIX filesystem API has a number of functions. **creat**, **stat**, **chown**, etc. In mergerfs these functions are grouped into 3 categories: **action**, **create**, and **search**. Functions and categories can be assigned a policy which dictates how **mergerfs** behaves. Any policy can be assigned to a function or category though some may not be very useful in practice. For instance: **rand** (random) may be useful for file creation (create) but could lead to very odd behavior if used for `chmod` (though only if there were more than one copy of the file).

56
man/mergerfs.1
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@ -1,7 +1,7 @@
.\"t
.\" Automatically generated by Pandoc 1.16.0.2
.\"
.TH "mergerfs" "1" "2017\-02\-18" "mergerfs user manual" ""
.TH "mergerfs" "1" "2017\-05\-26" "mergerfs user manual" ""
.hy
.SH NAME
.PP
@ -91,6 +91,11 @@ Please read more below before using.
\f[B]symlinkify\f[] behavior.
(default: 3600)
.IP \[bu] 2
\f[B]nullrw\f[]: turns reads and writes into no\-ops.
The request will succeed but do nothing.
Useful for benchmarking mergerfs.
(default: false)
.IP \[bu] 2
\f[B]fsname\f[]: sets the name of the filesystem as seen in
\f[B]mount\f[], \f[B]df\f[], etc.
Defaults to a list of the source paths concatenated together with the
@ -174,6 +179,55 @@ to the original drives or configure the software to follow symlinks if
such an option is available.
Alternatively create two mounts.
One for backup and one for general consumption.
.SS nullrw
.PP
Due to how FUSE works there is an overhead to all requests made to a
FUSE filesystem.
Meaning that even a simple passthrough will have some slowdown.
However, generally the overhead is minimal in comparison to the cost of
the underlying I/O.
By disabling the underlying I/O we can test the theoretical performance
boundries.
.PP
By enabling \f[C]nullrw\f[] mergerfs will work as it always does
\f[B]except\f[] that all reads and writes will be no\-ops.
A write will succeed (the size of the write will be returned as if it
were successful) but mergerfs does nothing with the data it was given.
Similarly a read will return the size requested but won\[aq]t touch the
buffer.
.PP
Example:
.IP
.nf
\f[C]
$\ dd\ if=/dev/zero\ of=/path/to/mergerfs/mount/benchmark\ ibs=1M\ obs=512\ count=1024
1024+0\ records\ in
2097152+0\ records\ out
1073741824\ bytes\ (1.1\ GB,\ 1.0\ GiB)\ copied,\ 15.4067\ s,\ 69.7\ MB/s
$\ dd\ if=/dev/zero\ of=/path/to/mergerfs/mount/benchmark\ ibs=1M\ obs=1M\ count=1024
1024+0\ records\ in
1024+0\ records\ out
1073741824\ bytes\ (1.1\ GB,\ 1.0\ GiB)\ copied,\ 0.219585\ s,\ 4.9\ GB/s
$\ dd\ if=/path/to/mergerfs/mount/benchmark\ of=/dev/null\ bs=512\ count=102400
102400+0\ records\ in
102400+0\ records\ out
52428800\ bytes\ (52\ MB,\ 50\ MiB)\ copied,\ 0.757991\ s,\ 69.2\ MB/s
$\ dd\ if=/path/to/mergerfs/mount/benchmark\ of=/dev/null\ bs=1M\ count=1024
1024+0\ records\ in
1024+0\ records\ out
1073741824\ bytes\ (1.1\ GB,\ 1.0\ GiB)\ copied,\ 0.18405\ s,\ 5.8\ GB/s
\f[]
.fi
.PP
It\[aq]s important to test with different \f[C]obs\f[] (output block
size) values since the relative overhead is greater with smaller values.
As you can see above the size of a read or write can massively impact
theoretical performance.
If an application performs much worse through mergerfs it could very
well be that it doesn\[aq]t optimally size its read and write requests.
.SH FUNCTIONS / POLICIES / CATEGORIES
.PP
The POSIX filesystem API has a number of functions.

1
src/config.cpp
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@ -43,6 +43,7 @@ namespace mergerfs
dropcacheonclose(false),
symlinkify(false),
symlinkify_timeout(3600),
nullrw(false),
POLICYINIT(access),
POLICYINIT(chmod),
POLICYINIT(chown),

1
src/config.hpp
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@ -51,6 +51,7 @@ namespace mergerfs
bool dropcacheonclose;
bool symlinkify;
time_t symlinkify_timeout;
bool nullrw;
public:
const Policy *policies[FuseFunc::Enum::END];

31
src/mergerfs.cpp
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@ -70,7 +70,8 @@ namespace local
static
void
get_fuse_operations(struct fuse_operations &ops,
const bool direct_io)
const bool direct_io,
const bool nullrw)
{
ops.flag_nullpath_ok = true;
#if FLAG_NOPATH
@ -110,11 +111,15 @@ namespace local
ops.open = mergerfs::fuse::open;
ops.opendir = mergerfs::fuse::opendir;
ops.poll = NULL;
ops.read = direct_io ?
mergerfs::fuse::read_direct_io :
mergerfs::fuse::read;
ops.read = (nullrw ?
mergerfs::fuse::read_null :
(direct_io ?
mergerfs::fuse::read_direct_io :
mergerfs::fuse::read));
#if READ_BUF
ops.read_buf = mergerfs::fuse::read_buf;
ops.read_buf = (nullrw ?
NULL :
mergerfs::fuse::read_buf);
#endif
ops.readdir = mergerfs::fuse::readdir;
ops.readlink = mergerfs::fuse::readlink;
@ -130,11 +135,15 @@ namespace local
ops.unlink = mergerfs::fuse::unlink;
ops.utime = NULL; /* deprecated; use utimens() */
ops.utimens = mergerfs::fuse::utimens;
ops.write = direct_io ?
mergerfs::fuse::write_direct_io :
mergerfs::fuse::write;
ops.write = (nullrw ?
mergerfs::fuse::write_null :
(direct_io ?
mergerfs::fuse::write_direct_io :
mergerfs::fuse::write));
#if WRITE_BUF
ops.write_buf = mergerfs::fuse::write_buf;
ops.write_buf = (nullrw ?
mergerfs::fuse::write_buf_null :
mergerfs::fuse::write_buf);
#endif
return;
@ -171,7 +180,9 @@ namespace mergerfs
mergerfs::options::parse(args,config);
local::setup_resources();
local::get_fuse_operations(ops,config.direct_io);
local::get_fuse_operations(ops,
config.direct_io,
config.nullrw);
return fuse_main(args.argc,
args.argv,

3
src/option_parser.cpp
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@ -190,6 +190,8 @@ parse_and_process_kv_arg(Config &config,
rv = parse_and_process(value,config.symlinkify);
else if(key == "symlinkify_timeout")
rv = parse_and_process(value,config.symlinkify_timeout);
else if(key == "nullrw")
rv = parse_and_process(value,config.nullrw);
}
if(rv == -1)
@ -291,6 +293,7 @@ usage(void)
" -o symlinkify_timeout=<int>\n"
" timeout in seconds before will turn to symlinks.\n"
" default=3600\n"
" -o nullrw=<bool> Disables reads and writes. For benchmarking.\n"
<< std::endl;
}

11
src/read.cpp
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@ -87,5 +87,16 @@ namespace mergerfs
return ::_read_direct_io(fi->fd,buf,count,offset);
}
int
read_null(const char *fusepath,
char *buf,
size_t count,
off_t offset,
fuse_file_info *ffi)
{
return count;
}
}
}

7
src/read.hpp
View File

@ -34,6 +34,13 @@ namespace mergerfs
size_t count,
off_t offset,
fuse_file_info *fi);
int
read_null(const char *fusepath,
char *buf,
size_t count,
off_t offset,
fuse_file_info *fi);
}
}

10
src/write.cpp
View File

@ -129,5 +129,15 @@ namespace mergerfs
{
return write(_write_direct_io,buf,count,offset,ffi);
}
int
write_null(const char *fusepath,
const char *buf,
size_t count,
off_t offset,
fuse_file_info *ffi)
{
return count;
}
}
}

7
src/write.hpp
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@ -34,6 +34,13 @@ namespace mergerfs
size_t count,
off_t offset,
fuse_file_info *fi);
int
write_null(const char *fusepath,
const char *buf,
size_t count,
off_t offset,
fuse_file_info *fi);
}
}

9
src/write_buf.cpp
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@ -99,6 +99,15 @@ namespace mergerfs
return rv;
}
int
write_buf_null(const char *fusepath,
fuse_bufvec *src,
off_t offset,
fuse_file_info *ffi)
{
return src->buf[0].size;
}
}
}

6
src/write_buf.hpp
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@ -30,6 +30,12 @@ namespace mergerfs
struct fuse_bufvec *buf,
off_t offset,
fuse_file_info *fi);
int
write_buf_null(const char *fusepath,
struct fuse_bufvec *buf,
off_t offset,
fuse_file_info *fi);
}
}