From 4e8da1958111796d55ad63b229ebd3ae6c54bf87 Mon Sep 17 00:00:00 2001 From: Nicolas Pitre Date: Mon, 15 May 2006 11:40:05 -0400 Subject: [PATCH] simple euristic for further free packing improvements Given that the early eviction of objects with maximum delta depth may exhibit bad packing on its own, why not considering a bias against deep base objects in try_delta() to mitigate that bad behavior. This patch adjust the MAX_size allowed for a delta based on the depth of the base object as well as enabling the early eviction of max depth objects from the object window. When used separately, those two things produce slightly better and much worse results respectively. But their combined effect is a surprising significant packing improvement. With this really simple patch the GIT repo gets nearly 15% smaller, and the Linux kernel repo about 5% smaller, with no significantly measurable CPU usage difference. Signed-off-by: Nicolas Pitre Signed-off-by: Junio C Hamano --- pack-objects.c | 7 ++----- 1 file changed, 2 insertions(+), 5 deletions(-) diff --git a/pack-objects.c b/pack-objects.c index 5466b15167..526c090c61 100644 --- a/pack-objects.c +++ b/pack-objects.c @@ -1039,8 +1039,8 @@ static int try_delta(struct unpacked *trg, struct unpacked *src, /* Now some size filtering euristics. */ size = trg_entry->size; - max_size = size / 2 - 20; - if (trg_entry->delta) + max_size = (size/2 - 20) / (src_entry->depth + 1); + if (trg_entry->delta && trg_entry->delta_size <= max_size) max_size = trg_entry->delta_size-1; src_size = src_entry->size; sizediff = src_size < size ? size - src_size : 0; @@ -1129,15 +1129,12 @@ static void find_deltas(struct object_entry **list, int window, int depth) if (try_delta(n, m, m->index, depth) < 0) break; } -#if 0 /* if we made n a delta, and if n is already at max * depth, leaving it in the window is pointless. we * should evict it first. - * ... in theory only; somehow this makes things worse. */ if (entry->delta && depth <= entry->depth) continue; -#endif idx++; if (idx >= window) idx = 0; -- 2.43.2