On 10/9/2019 7:44 PM, Jonathan Tan wrote:
> Instead, recompute ancestry if we ever need to reclaim memory.
I find this message lacking in important details:
1. Where do we recompute ancestry?
2. What are the performance implications of this change?
3. Why is it important that you construct a stack of deltas in
prune_base_data()?
> Signed-off-by: Jonathan Tan <jonathanta...@google.com>
> ---
> builtin/index-pack.c | 41 ++++++++++++++++++++++-------------------
> 1 file changed, 22 insertions(+), 19 deletions(-)
>
> diff --git a/builtin/index-pack.c b/builtin/index-pack.c
> index 99f6e2957f..35f7f9e52b 100644
> --- a/builtin/index-pack.c
> +++ b/builtin/index-pack.c
> @@ -34,7 +34,6 @@ struct object_stat {
>
> struct base_data {
> struct base_data *base;
> - struct base_data *child;
> struct object_entry *obj;
> void *data;
> unsigned long size;
> @@ -44,7 +43,6 @@ struct base_data {
>
> struct thread_local {
> pthread_t thread;
> - struct base_data *base_cache;
> size_t base_cache_used;
> int pack_fd;
> };
> @@ -380,27 +378,37 @@ static void free_base_data(struct base_data *c)
> }
> }
>
> -static void prune_base_data(struct base_data *retain)
> +static void prune_base_data(struct base_data *youngest_child)
> {
> struct base_data *b;
> struct thread_local *data = get_thread_data();
> - for (b = data->base_cache;
> - data->base_cache_used > delta_base_cache_limit && b;
> - b = b->child) {
> - if (b->data && b != retain)
> - free_base_data(b);
> + struct base_data **ancestry = NULL;
> + int nr = 0, alloc = 0;
> + int i;
> +
> + if (data->base_cache_used <= delta_base_cache_limit)
> + return;
> +
> + /*
> + * Free all ancestors of youngest_child until we have enough space,
> + * starting with the oldest. (We cannot free youngest_child itself.)
> + */
> + for (b = youngest_child->base; b != NULL; b = b->base) {
> + ALLOC_GROW(ancestry, nr + 1, alloc);
> + ancestry[nr++] = b;
> + }
> + for (i = nr - 1;
> + i >= 0 && data->base_cache_used > delta_base_cache_limit;
> + i--) {
> + if (ancestry[i]->data)
> + free_base_data(ancestry[i]);
> }
> + free(ancestry);
> }
>
> static void link_base_data(struct base_data *base, struct base_data *c)
> {
> - if (base)
> - base->child = c;
> - else
> - get_thread_data()->base_cache = c;
> -
> c->base = base;
> - c->child = NULL;
> if (c->data)
> get_thread_data()->base_cache_used += c->size;
> prune_base_data(c);
> @@ -408,11 +416,6 @@ static void link_base_data(struct base_data *base,
> struct base_data *c)
>
> static void unlink_base_data(struct base_data *c)
> {
> - struct base_data *base = c->base;
> - if (base)
> - base->child = NULL;
> - else
> - get_thread_data()->base_cache = NULL;
> free_base_data(c);
> }
Seems like this method should be removed and all callers should
call free_base_data() instead.
-Stolee
