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d4b3836493
ExtentWalker doesn't gain significant benefits from caching, and the extra SEARCH_V2 ioctls were blamed for a 33% kernel CPU overhead by perf. Reduce the number of extents to 16 in lieu of fixing the caching. This gives a significant speed boost on CPU-bound workloads compared to the original 1024--almost 40% faster on a single SSD with a filesystem consisting of raw VM images mounted with compress=zstd. This also seems to reduce LOGICAL_INO overhead. Perhaps SEARCH_V2 and LOGICAL_INO were trying to lock the same extents, and interfering with each other? Signed-off-by: Zygo Blaxell <bees@furryterror.org>
104 lines
2.5 KiB
C++
104 lines
2.5 KiB
C++
#ifndef CRUCIBLE_EXTENTWALKER_H
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#define CRUCIBLE_EXTENTWALKER_H
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#include "crucible/fd.h"
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namespace crucible {
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using namespace std;
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// FIXME: ExtentCursor is probably a better name
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struct Extent {
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off_t m_begin = 0;
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off_t m_end = 0;
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uint64_t m_physical = 0;
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uint64_t m_flags = 0;
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// Btrfs extent reference details
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off_t m_physical_len = 0;
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off_t m_logical_len = 0;
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off_t m_offset = 0;
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// fiemap flags are uint32_t, so bits 32..63 are OK for us
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// no extent here
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static const uint64_t HOLE = (1ULL << 32);
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// extent is physical space full of zeros
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static const uint64_t PREALLOC = (1ULL << 33);
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// extent's physical (RAM) size does not match logical (can we know this?)
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static const uint64_t OBSCURED = (1ULL << 34);
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operator bool() const;
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off_t size() const;
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off_t begin() const { return m_begin; }
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off_t end() const { return m_end; }
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uint64_t flags() const { return m_flags; }
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uint64_t physical() const { return m_physical; }
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off_t physical_len() const { return m_physical_len; }
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off_t logical_len() const { return m_logical_len; }
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off_t offset() const { return m_offset; }
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bool compressed() const;
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uint64_t bytenr() const;
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bool operator==(const Extent &that) const;
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bool operator!=(const Extent &that) const { return !(*this == that); }
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Extent() = default;
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Extent(const Extent &e) = default;
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};
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class ExtentWalker {
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public:
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using Vec = vector<Extent>;
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using Itr = Vec::iterator;
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protected:
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Fd m_fd;
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Stat m_stat;
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virtual Vec get_extent_map(off_t pos);
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static const unsigned sc_extent_fetch_max = 16;
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static const unsigned sc_extent_fetch_min = 4;
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static const off_t sc_step_size = 0x1000 * (sc_extent_fetch_max / 2);
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private:
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Vec m_extents;
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Itr m_current;
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Itr find_in_cache(off_t pos);
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void run_fiemap(off_t pos);
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public:
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ExtentWalker(Fd fd = Fd());
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ExtentWalker(Fd fd, off_t initial_pos);
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virtual ~ExtentWalker();
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void reset();
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Extent current();
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bool next();
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bool prev();
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void seek(off_t new_pos);
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friend ostream & operator<<(ostream &os, const ExtentWalker &ew);
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};
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class BtrfsExtentWalker : public ExtentWalker {
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uint64_t m_tree_id;
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Fd m_root_fd;
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protected:
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Vec get_extent_map(off_t pos) override;
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public:
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BtrfsExtentWalker(Fd fd);
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BtrfsExtentWalker(Fd fd, off_t initial_pos);
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BtrfsExtentWalker(Fd fd, off_t initial_pos, Fd root_fd);
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void set_root_fd(Fd fd);
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};
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ostream &operator<<(ostream &os, const Extent &e);
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};
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#endif // CRUCIBLE_EXTENTWALKER_H
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