Rewrite the text related to 'btrfs send' to clarify that the send
workaround is no longer necessary to avoid kernel crashes, but still
useful because send and dedupe still do not work at the same time.
Replace "many backref code changes" with a specific commit reference,
and improve the grammar of some issue descriptions.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
Apparently there's Github Flavored Markdown, and there's the markup
language that github uses, and they are distinct things.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
Present known kernel bugs in table form with issue descriptions,
fixed and broken kernel versions, and references to fixes.
Update kernel version recommendations to include information on kernel
versions up to 5.8.14.
Reduce emphasis on data corruption bugs which are 1) two or more
years old now, and 2) much less bad than the bugs in kernel 5.1.
Add deprecation warning for kernels before 4.15.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
Prefer to use cmark-gfm with extension 'table' so we can use tables in
locally-generated HTML files. If cmark-gfm is not installed then
fall back to some other Markdown implemeentation, but the tables will
be broken on every other implementation I have tried so far.
Also make the HTML output depend on the Makefile, since there may be
document translation options specified there (like '-e table' or an
entirely different Markdown implementation).
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
uncaught_exception() had only the one valid use case, and it can be
reimplemented by literally calling current_exception() instead.
current_exception() has several valid use cases, so it is not likely
to be deprecated any time soon.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
We cannot use BeesContext::roots() until after
BeesContext::set_root_path() has been called.
Save up the parameter settings until then.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
"Storm of softlockups" starts with a simple BUG_ON, but after the
BUG_ON, all cores that are waiting on spinlocks get stuck.
The _first_ kernel call trace is required to identify the bug.
At least two such bugs have been identified.
Add some notes about the conflict between LOGICAL_INO and balance,
and the recently added bees workaround.
Update the gotchas page for balances to point to the kernel bugs page.
Remove "bees and the full balance will both work correctly" as that
statement is not true.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
This avoids some kernel bugs. One of them is fixed in 5.3.4 and later:
efad8a853a "Btrfs: fix use-after-free when using the tree modification log"
There are apparently others in current kernels, so for now just put bees
on pause until the balance is done.
At some point we may want to provide an option to disable this
workaround; however, running bees and balance at the same time makes
neither particularly fast, so maybe we'll just leave it this way.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
Saying just "This feature" at some log levels could be puzzling. Let's
remove this message, the feature works without problems for a year.
Signed-off-by: Kai Krakow <kai@kaishome.de>
In version 2.30 glibc added it's own gettid() function. This resulted in
"error: call of overloaded ‘gettid()’ is ambiguous" because gettid()
now exists in both namespace crucible and std.
For now, use explicit references to namespace crucible. This continues
to work with new and old libc without having to test specific library
versions.
At some point, glibc gettid() will be deployed widely enough that we can
remove the crucible version entirely.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
Localize the hash function in bees to a single spot to make it easier
to change later (or at runtime).
Remove some code that was using a property of CRC as an optimization.
The optimization doesn't work for other hash functions, and running the
CRC function takes more CPU time than the optimization saved.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
CityHash64 appears to be the fastest available block hashing algorithm
that is good enough for dedupe. It takes much less CPU than the CRC64
function, and avoids hash-collision problems with file formats that use
CRC64 as an integrity check on 4K block boundaries.
Extracted from git://github.com/google/cityhash with the "CRC" hash
functions (which require Intel/AMD CPU support) removed. We don't
need those, and they introduce a new (if only theoretical) build-time
dependency.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
We got away with this because GCC 4.8 (and apparently every GCC prior
to 9) didn't notice or care, and because there is nothing referenced
inside the lambda function body that isn't accessible from any other
kind of function body (i.e. the capture wasn't needed at all).
GCC 9 now enforces what the C++ standard said all along: there is
no need to allow capture-default in this case, so it is not.
Fix by removing the offending capture-default.
Fixes: https://github.com/Zygo/bees/issues/112
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
It is not possible to emulate extent-same by clone in a safe way.
EXTENT_SAME has been supported in btrfs since kernel 3.13, which
is much too old to contemplate running bees on.
Remove this dangerous and unused function.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
We are getting a lot of exceptions when an inline extent is too large for the
TREE_SEARCH_V2 buffer. This disrupts ExtentWalker's extent boundary
search when there is an inline extent at the beginning of a file:
# fiemap foo
Log 0x0..0x1000 Phy 0x0..0x1000 Flags FIEMAP_EXTENT_NOT_ALIGNED|FIEMAP_EXTENT_DATA_INLINE
Log 0x1000..0x2000 Phy 0x7307f9000..0x7307fa000 Flags 0
Log 0x2000..0x3000 Phy 0x731078000..0x731079000 Flags 0
Log 0x3000..0x5000 Phy 0x73127d000..0x73127f000 Flags FIEMAP_EXTENT_ENCODED
Log 0x5000..0x6000 Phy 0x73137a000..0x73137b000 Flags 0
Log 0x6000..0x7000 Phy 0x731683000..0x731684000 Flags 0
Log 0x7000..0x8000 Phy 0x73224f000..0x732250000 Flags 0
Log 0x8000..0x9000 Phy 0x7323c9000..0x7323ca000 Flags 0
Log 0x9000..0xb000 Phy 0x732425000..0x732427000 Flags FIEMAP_EXTENT_ENCODED
Log 0xb000..0xc000 Phy 0x732598000..0x732599000 Flags 0
Log 0xc000..0xd000 Phy 0x7325d5000..0x7325d6000 Flags FIEMAP_EXTENT_LAST
# fiewalk foo
exception type std::system_error: BTRFS_IOC_TREE_SEARCH_V2: /tmp/foo at fs.cc:844: Value too large for defined data type
Normally crawlers simply skip over inline extents, but ExtentWalker will
seek backward from the first non-inline extent to confirm that it has
an accurate starting block for the target extent. This fails when it
encounters the first inline extent.
strace reveals that buffer size is too small for the first extent,
as seen here:
ioctl(3, BTRFS_IOC_TREE_SEARCH_V2, {key={tree_id=258, min_objectid=78897856, max_objectid=UINT64_MAX, min_offset=0, max_offset=UINT64_MAX, min_transid=0, max_transid=UINT64_MAX, min_type=BTRFS_EXTENT_DATA_KEY, max_type=BTRFS_EXTENT_DATA_KEY, nr_items=16}, buf_size=1360} => {buf_size=1418}) = -1 EOVERFLOW (Value too large for defined data type)
Fix this by increasing the buffer size until it can handle the largest
possible object on the largest possible btrfs metadata page (65536 bytes).
BtrfsExtentWalker already has optimizations to minimize the allocation
cost, so we don't need any changes there.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
Some build environments (ARM? AARCH64?) do not have the fields
si_lower and si_upper in siginfo.
bees doesn't need them, so don't try to access them.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
Update the version ranges on the dependencies.
FIXME/TODO: start dropping early versions that don't work with current
code?
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
flushoncommit or not-flushoncommit isn't really a bees matter--it's
a sysadmin's tradeoff between reliability and performance. bees does
not affect that tradeoff because all dedupe src extents are flushed, so
bees introduces no *new* data loss risks in the noflushoncommit
case--i.e. any data that you could lose while running bees, you'd also
lose when not running bees.
Note that the converse is not true: bees might trigger flushing on
data that would not normally have been flushed with noflushoncommit,
and improve data integrity after a crash as a side-effect of dedupe
operations. The risks of noflushoncommit might be reduced by running
bees. I don't have evidence based on experimental data to support that
conclusion, so I'll just leave this possibility as a rumor in a commit
log message.
lvmcache can be moved from the "bad" list to the "good" list now.
bcache remains in the "bad" list due to some non-data-losing failures
that only seem to happen with bcache.
Add a note about CPUs with strange endianness or page sizes, as nobody
seems to have tried those.
Remove "at great cost" from the btrfs send workaround. The cost is
the cost, there is no need to editorialize.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
The existence of information about known data corruption bugs should be
visible from the top-level page.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
* comprehensive list of kernels with bees-triggered corruption bug fixes
* deadlock between dedupe and rename is now fixed (in some places)
* compressed data corruption is now fixed (in more places)
* btrfs send fix for one bug is now merged in 5.2-rc1, another bug remains
* retired the bcache/lvmcache bug (can't reproduce those bugs any more,
although I *can* reproduce an interesting non-destructive bcache bug)
* new minor bug entries for two harmless kernel warnings
* new entry for storm-of-soft-lockups
Fixes: https://github.com/Zygo/bees/issues/107
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
This is especially useful when dynamic load management allocates more
worker threads than active tasks, so the extra threads are effectively
invisible.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
This may help users understand some of the things that happen inside
bees...or it may just be horribly long and confusing.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
Enable much simpler Task management: each time a Task needs to be done
at least once in the future, simply invoke the run() method on the Task.
The Task will ensure that it only runs once, only appears in a queue
once, and will run again if a run request is made while the Task is
already running.
Make the queue policy a member of the Task rather than a method. This
enables Tasks to reschedule themselves, possibly on the appropriate queue
if we have more than one of those some day.
This happens to make Tasks more similar to Linux kernel workers.
This similarity is coincidental, but not undesirable.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
Introduce a mechanism to suppress exceptions which do not produce a
full stack trace for common known cases where a loop should be aborted.
Use this mechanism to suppress the infamous "FIXME" exception.
Reduce the log level to at most NOTICE, and in some cases DEBUG.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
SIGUNUSED is not defined in many environments (it seems to be defined
in only one I've tried so far). Hide the reference with #ifdef.
Fixes: https://github.com/Zygo/bees/issues/94
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
libcrucible at one time in the distant past had to be a shared library
to force global C++ object initialization; however, this is no longer
required.
Make libcrucible static to solve various rpath and soname versioning
issues, especially when distros try (unwisely) to package the library
separately.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
We stopped supporting shared hash tables a long time ago. Remove comments
describing the behavior of shared hash tables.
Add an event counter for pushing a hash to the front when it is already at
the front.
Audited the code for a bug related to bucket handling that impairs space
efficiency when the bucket size is greater than 1. Didn't find one.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
Capture SIGINT and SIGTERM and shut down, preserving current completed
crawl and hash table state.
* Executing tasks are completed, queued tasks are paused.
* Crawl state is saved.
* The crawl master and crawl writeback threads are terminated.
* The task queue is flushed.
* Dirty hash table extents are flushed.
* Hash prefetch and writeback threads are terminated.
* Hash table is deallocated.
* FD caches and tmpfiles are destroyed.
* Assuming the above didn't crash or deadlock, bees exits.
The above order isn't the fastest, but it does roughly follow the
shared_ptr dependencies and avoids data races--especially those that
might lead to bees reporting an extent scanned when it was only queued
for future scanning that did not occur.
In case of a violation of expected shared_ptr dependency order,
exceptions in BeesContext child object accessor methods (i.e. roots(),
hash_table(), etc) prevent any further progress in threads that somehow
remain unexpectedly active.
Move some threads from main into BeesContext so they can be stopped
via BeesContext. The main thread now runs a loop waiting for signals.
A slow FD leak was discovered in TempFile handling. This has not been
fixed yet, but an implementation detail of the C++ runtime library makes
the leak so slow it may never be important enough to fix.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
We need to replace nanosleeps with condition variables so that we
can implement BeesContext::stop. Export the time calculation from
sleep_for() into a new method called sleep_time().
If the thread executing RateLimiter::sleep_for() is interrupted, it will
no longer be able to restart, as the sleep_time() method is destructive.
This calls for further refactoring of sleep_time() into destructive
and non-destructive parts; however, there are currently no users of
sleep_for() which rely on being able to restart after being interrupted
by a signal.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
Add a method to have TaskMaster discard any entries in its queue, terminate
all worker threads, and prevent any new Tasks from being queued.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
The deadlock seems to be fixed now (if there ever was one--there certainly
were deadlocks, but matching deadlocks to root causes is non-trivial
and a number of distinct deadlock cases have been fixed in recent years).
The benchmark data is inconclusive about whether it is better to fsync or
not to fsync. A paranoia option might be useful here.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
The crawl_master task had a simple atomic variable that was supposed
to prevent duplicate crawl_master tasks from ending up in the queue;
however, this had a race condition that could lead to m_task_running
being set with no crawl_master task running to clear it. This would in
turn prevent crawl_thread from scheduling any further crawl_master tasks,
and bees would eventually stop doing any more work.
A proper fix is to modify the Task class and its friends such that
Task::run() guarantees that 1) at most one instance of a Task is ever
scheduled or running at any time, and 2) if a Task is scheduled while
an instance of the Task is running, the scheduling is deferred until
after the current instance completes. This is part of a fairly large
planned change set, but it's not ready to push now.
So instead, unconditionally push a new crawl_master Task into the queue
on every poll, then silently and quickly exit if the queue is too full
or the supply of new extents is empty. Drop the scheduling-related
members of BeesRoots as they will not be needed when the proper fix lands.
Fixes: 4f0bc78a "crawl: don't block a Task waiting for new transids"
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
If /bin/sh is bash, the 'type' builtin produces a list of filenames
that match the arguments to $PATH.
If /bin/sh is dash, we get errors like:
/bin/sh: 1: P:: not found
Hopefully having a build-dep on bash is not controversial.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
The two files are identical except README.md links to docs/* while
index.md links to *.
A sed script can do that transformation, so use sed to do it.
This does modify a file in git, but this is necessary to make all
the Github views work consistently.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
This sequence of log messages isn't clear:
crawl_master: WORKAROUND: Avoiding RO subvol 6094
crawl_master: WORKAROUND: RO root 6094
The first is from a cache miss, and appears wherever a root is opened
(dedupe or crawl). The second is skipping an entire subvol scan, and
only happens in crawl_master.
Elaborate on the second message a little.
Also use the term "root" consistently when referring to subvol tree IDs.
btrfs refers to these objects by (at least) three distinct names: tree,
subvol, and root. Using three different words for the same thing is worse
than using a single wrong word consistently to refer to the same concept.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
After weeks of testing I copied part of a change to main without copying
the rest of the change, leading to an immediate segfault on startup.
So here is the rest of the change: limit the number of
BeesContexts per process to 1. This change was discussed at
https://github.com/Zygo/bees/issues/54#issuecomment-360332529 but there
are more reasons to do it now: the candidates to replace the current
hash table format are less forgiving of sharing hash tables, and it may
even become necessary to have more than one hash table per BeesContext
instance (e.g. to keep datasum and nodatasum data separate).
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
https://github.com/Zygo/bees/issues/91 describes problems encountered
when running bees on systems with many CPU cores.
Limit the computed number of threads (using --thread-factor or the
default) to a maximum of 8 (i.e. the number of logical cores in a modern
laptop). Users can override the limit by using --thread-count.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
options.md was a disorganized mess that markdown couldn't parse properly.
Break the options list down into sections by theme. Add the new
'--workaround-btrfs-send' option to the new 'Workarounds' section.
Clean up the rest of the text and fix some inconsistencies.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
