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btrsame: a dump of random updates from 2020-2021
There isn't really a coherent development plan for this tool. It is more of a proving ground for various bees concepts, and occasionally useful for spot dedupe of single large files that are known to be mostly duplicate. It's published here because occasionally a few lines of this code become useful for explaining to people how to implement better tools. In particular, btrsame has no concept of btrfs's requirements for extent splitting, so it will be ineffective as a dedupe tool for files that are similar but not entirely identical. Not only that, btrsame may also create a potentially large number of unreachable blocks in the process. Change summary: - opens files O_RDONLY when using dedupe_file_range ioctl - drop the code that implements the contiguous differences threshold. - shorten status line by pretty-printing numbers with a unit suffix - don't throw an error exception while in the process of formatting a message about the error - use readahead to work around dedupe ioctl behavior - remove random notes about now-long-dead lockup bugs - remove long dead commented out file reference lookup tool Signed-off-by: Zygo Blaxell <bees@furryterror.org>
This commit is contained in:
Zygo Blaxell
parent
02008260f7
commit
fa04c10ddd
158
src/btrsame.cc
158
src/btrsame.cc
@ -6,6 +6,7 @@
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#include <algorithm>
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#include <cassert>
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#include <cmath>
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#include <cstring>
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#include <iostream>
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#include <set>
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@ -23,6 +24,7 @@ using namespace std;
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#define EXTENT_SAME_CLASS BtrfsExtentSame
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static const bool ALWAYS_ALIGN = false;
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static const bool OPEN_RDONLY = true;
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static const int EXTENT_ALIGNMENT = 4096;
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@ -34,9 +36,6 @@ const off_t max_step_size = 128 * 1024 * 1024;
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// Not a good idea to go below 4K
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const off_t min_step_size = 4096;
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// Give up fairly early - 1MB
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const off_t max_contiguous_differences = 1 * 1024 * 1024;
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struct PhysicalBlockRange {
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uint64_t m_start, m_end;
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@ -89,7 +88,23 @@ verbose()
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}
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static
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bool
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string
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pretty(double d)
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{
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static const char * units[] = { "", "K", "M", "G", "T", "P", "E" };
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static const char * *units_stop = units + sizeof(units) / sizeof(units[0]) - 1;
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const char * *unit = units;
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while (d >= 1024 && unit < units_stop) {
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d /= 1024;
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++unit;
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}
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ostringstream oss;
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oss << (round(d * 1000.0) / 1000.0) << *unit;
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return oss.str();
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}
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static
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void
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bees_same_file(Fd incumbent_fd, Fd candidate_fd)
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{
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Stat incumbent_stat(incumbent_fd);
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@ -110,15 +125,18 @@ bees_same_file(Fd incumbent_fd, Fd candidate_fd)
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off_t total_deduped = 0;
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int status_ok = 0, status_err = 0, status_different = 0;
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off_t step_size = max_step_size;
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uint64_t contiguous_differences = 0;
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uint64_t total_differences = 0;
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uint64_t total_shared = 0;
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uint64_t total_holes = 0;
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bool fatal_error = false;
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off_t p, len;
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vector<uint8_t> silly_buffer(max_step_size);
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off_t p;
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off_t len = 0;
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ostringstream oss;
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Timer elapsed;
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Timer timer;
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for (p = 0; p < common_size && !fatal_error; ) {
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off_t this_step_size = step_size;
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@ -130,14 +148,15 @@ bees_same_file(Fd incumbent_fd, Fd candidate_fd)
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}
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oss.str("");
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oss << "\r"
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<< "total " << common_size
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<< (total_deduped ? " **DUP** " : " dup ") << total_deduped
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<< " diff " << total_differences
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<< " shared " << total_shared
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<< " holes " << total_holes
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<< " off " << p
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<< " len " << len
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<< ' ';
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<< "total " << pretty(common_size)
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<< (total_deduped ? " **DUP** " : " dup ") << pretty(total_deduped)
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<< " diff " << pretty(total_differences)
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<< " shared " << pretty(total_shared)
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<< " holes " << pretty(total_holes)
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<< " off " << pretty(p)
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<< " len " << pretty(len)
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<< " elapsed " << elapsed
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<< " \b\b\b";
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PhysicalBlockRange incumbent_pbr(incumbent_fd, p, len);
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PhysicalBlockRange candidate_pbr(candidate_fd, p, len);
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@ -146,42 +165,37 @@ bees_same_file(Fd incumbent_fd, Fd candidate_fd)
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off_t shared_len = min(incumbent_pbr.m_end - incumbent_pbr.m_start, candidate_pbr.m_end - candidate_pbr.m_start);
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this_step_size = max(min_step_size, min(shared_len, common_size - p));
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total_shared += this_step_size;
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contiguous_differences = 0;
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len = shared_len;
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// At this point, if we see anything shared, it's because we already deduped the whole thing
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// unless it's a hole. We do have those.
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if (incumbent_pbr.m_start) {
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// break;
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} else {
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if (!incumbent_pbr.m_start) {
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total_holes += shared_len;
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}
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} else {
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// These might be triggering a locking bug
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// ...actually we found the locking bug and it's somewhere else
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// ...though there may be a memory leak bug so let's try turning this back off again
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// ...nope, seems to be a kernel bug triggered by git
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// ...but we still run out of RAM, hard, on some machines running this code. But not all.
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// ...let's avoid the scary syscalls until we prove they work, OK?
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// ...ok let's go looking for scary syscall behavior now
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// ...no hangs but they don't seem to be helping, or are helping negatively
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// ...long stalls here, see if they go away
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// OK we were totally doing the wrong thing here. "common_size - p", indeed.
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// DIE_IF_MINUS_ONE(posix_fadvise(incumbent_fd, p, common_size - p, POSIX_FADV_WILLNEED));
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// DIE_IF_MINUS_ONE(posix_fadvise(candidate_fd, p, common_size - p, POSIX_FADV_WILLNEED));
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DIE_IF_MINUS_ONE(readahead(incumbent_fd, p, len));
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DIE_IF_MINUS_ONE(readahead(candidate_fd, p, len));
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// The above kernel calls request readahead, same as posix_fadvise ... MADV_WILLNEED
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// but in btrfs the readahead iops are scheduled at idle priority.
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// This is not what we want, so here we can use read to force non-idle priority
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// (or just use a scheduler that doesn't support io priority).
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// DIE_IF_MINUS_ONE(pread(incumbent_fd, silly_buffer.data(), len, p));
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// DIE_IF_MINUS_ONE(pread(candidate_fd, silly_buffer.data(), len, p));
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EXTENT_SAME_CLASS bes(incumbent_fd, p, len);
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bes.add(candidate_fd, p);
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bes.do_ioctl();
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// Don't need it any more, might either speed up page reclaim, or
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// make us block waiting for writeback.
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DIE_IF_MINUS_ONE(posix_fadvise(incumbent_fd, p, len, POSIX_FADV_DONTNEED));
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DIE_IF_MINUS_ONE(posix_fadvise(candidate_fd, p, len, POSIX_FADV_DONTNEED));
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int status = bes.m_info[0].status;
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if (status == 0) {
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++status_ok;
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total_deduped += bes.m_info[0].bytes_deduped;
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contiguous_differences = 0;
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if (step_size * 2 <= max_step_size) {
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step_size *= 2;
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}
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@ -191,9 +205,8 @@ bees_same_file(Fd incumbent_fd, Fd candidate_fd)
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++status_err;
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switch (-status) {
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case EXDEV:
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oss << " (fatal error)" << endl;
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THROW_ERRNO(-status);
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break;
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oss << " (fatal error, paths are not on the same mount point?)" << endl;
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return;
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}
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} else if (status == BTRFS_SAME_DATA_DIFFERS) {
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++status_different;
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@ -205,12 +218,6 @@ bees_same_file(Fd incumbent_fd, Fd candidate_fd)
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continue;
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} else {
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total_differences += step_size;
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contiguous_differences += step_size;
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if (total_deduped == 0 && contiguous_differences > max_contiguous_differences) {
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oss << " (giving up, contiguous_differences = " << contiguous_differences
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<< ", max_contiguous_differences = " << max_contiguous_differences << ")" << endl;
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break;
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}
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}
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}
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}
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@ -218,17 +225,16 @@ bees_same_file(Fd incumbent_fd, Fd candidate_fd)
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p += len;
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}
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cerr << oss.str() << "\r"
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<< "total " << common_size
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<< (total_deduped ? " **DUP** " : " dup ") << total_deduped
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<< " diff " << total_differences
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<< " shared " << total_shared
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<< " holes " << total_holes
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<< " off " << p
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<< " len " << len
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<< "total " << pretty(common_size)
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<< (total_deduped ? " **DUP** " : " dup ") << pretty(total_deduped)
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<< " diff " << pretty(total_differences)
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<< " shared " << pretty(total_shared)
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<< " holes " << pretty(total_holes)
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<< " off " << pretty(p)
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<< " len " << pretty(len)
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<< " elapsed " << elapsed
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<< " "
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<< endl;
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return status_ok > 0 && status_err == 0 && status_different == 0;
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}
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int
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@ -248,56 +254,10 @@ main(int argc, char **argv)
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if (verbose()) {
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cerr << "B: " << argv[2] << endl;
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}
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Fd candidate_fd = open_or_die(argv[2], O_RDWR);
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Fd candidate_fd = open_or_die(argv[2], OPEN_RDONLY ? O_RDONLY : O_RDWR);
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int rv;
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if (bees_same_file(incumbent_fd, candidate_fd)) {
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rv = EXIT_SUCCESS;
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} else {
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// any run that doesn't end with terminate() is success
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// rv = EXIT_FAILURE;
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rv = EXIT_SUCCESS;
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}
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bees_same_file(incumbent_fd, candidate_fd);
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// Let's try not doing this to see if our memory leaks go away
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// OK we have memory leak fixes, bring on the extra testing
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// OK it's slow and unnecessary in this context
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#if 0
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catch_all([&]() {
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PhysicalBlockRange pbr(incumbent_fd, 0);
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cerr << "pbr = " << to_hex(pbr.m_start) << ".." << to_hex(pbr.m_end) << endl;
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set<uint64_t> inodes_seen;
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set<string> paths_seen;
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if (pbr.m_start) {
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BtrfsIoctlLogicalInoArgs lia(pbr.m_start);
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lia.do_ioctl(incumbent_fd);
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// cerr << &lia;
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// [0] = BtrfsInodeOffsetRoot { .m_inum = 10544359, .m_offset = 0x0, .m_root = 257},
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for (auto i : lia.m_iors) {
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auto seen_inode = inodes_seen.insert(i.m_inum);
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if (!seen_inode.second) {
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continue;
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}
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cerr << "Root " << i.m_root << " Inode " << i.m_inum << " Offset " << to_hex(i.m_offset) << "\n";
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catch_all([&]() {
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// cerr << "Inode " << i.m_inum << ":\n";
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BtrfsIoctlInoPathArgs ipa(i.m_inum);
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ipa.do_ioctl(incumbent_fd);
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for (auto p : ipa.m_paths) {
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auto seen_path = paths_seen.insert(p);
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if (seen_path.second) {
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cerr << "\tPath " << p << "\n";
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}
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}
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// Not useful without the rest of the root tree
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// BtrfsIoctlInoLookupArgs ila(BTRFS_FIRST_FREE_OBJECTID);
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// ila.do_ioctl(incumbent_fd);
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// cerr << "ila = '" << ila.name << "'\n";
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});
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}
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}
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});
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#endif
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return rv;
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// any run that doesn't end with terminate() is success,
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return EXIT_SUCCESS;
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}
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