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extentwalker: fix the binary search and add some debug infrastructure

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Add some conditionally-compiled debug code, including an in-memory log
of what ExtentWalker does.  Dump that log on exceptions.

If we loop too many times in a debug build, kill the process so we can
stack trace.  In non-debug builds just throw a normal exception.

Grow the step size instead of shrinking it, to reduce the number of
binary search iterations.

Prevent a bug where the step size bottoms out before positioning the
target extent in the middle of the result vector.

Use the first extent for "first_extent", instead of the 3rd.

Get rid of some redundant checks.

Signed-off-by: Zygo Blaxell <bees@furryterror.org>
This commit is contained in:
Zygo Blaxell
2021-06-01 20:06:54 -04:00
parent 54f03a0297
commit 6adaedeecd
2 changed files with 82 additions and 55 deletions
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8
include/crucible/extentwalker.h
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@ -58,10 +58,6 @@ namespace crucible {
virtual Vec get_extent_map(off_t pos);
static const unsigned sc_extent_fetch_max = 16;
static const unsigned sc_extent_fetch_min = 4;
static const off_t sc_step_size = 0x1000 * (sc_extent_fetch_max / 2);
private:
Vec m_extents;
Itr m_current;
@ -69,6 +65,10 @@ namespace crucible {
Itr find_in_cache(off_t pos);
void run_fiemap(off_t pos);
#ifdef EXTENTWALKER_DEBUG
ostringstream m_log;
#endif
public:
ExtentWalker(Fd fd = Fd());
ExtentWalker(Fd fd, off_t initial_pos);