5c49c11686
With large amount of objects, check_object() is really trashing the pack
sliding map and the filesystem cache. It has a completely random access
pattern especially with old objects where delta replay jumps back and
forth all over the pack.
This patch improves things by:
1) sorting objects by their offset in pack before calling check_object()
so the pack access pattern is linear;
2) recording the object type at add_object_entry() time since it is
already known in most cases;
3) recording the pack offset even for preferred_base objects;
4) avoid calling sha1_object_info() if all possible.
This limits pack accesses to the bare minimum and makes them perfectly
linear.
In the process check_object() was made more clear (to me at least).
Note: I thought about walking the sorted_by_offset list backward in
get_object_details() so if a pack happens to be larger than the available
file cache, then the cache would have been populated with useful data from
the beginning of the pack already when find_deltas() is called. Strangely,
testing (on Linux) showed absolutely no performance difference.
Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>
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