Re: [PATCH 3/6] Check 'may_checkpoint()' early

["Serge E. Hallyn" <serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>]

Quoting Sukadev Bhattiprolu (sukadev-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org):
> 
> Oren, 
> 
> I see that patch 3/6 (deny external checkpoint unless frozen) in this
> set was merged in v14, but do you have any plans/objections to merging
> this optimization patch ? Serge had acked an earlier version of this
> patch.
> 
> Suka
> 
> Sukadev Bhattiprolu [sukadev-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org] wrote:
> | 
> | From: Sukadev Bhattiprolu <sukadev-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>
> | Date: Thu, 12 Mar 2009 14:19:54 -0700
> | Subject: [PATCH 3/6] Check 'may_checkpoint()' early
> | 
> | We currently check if a task is checkpointable when writing the task
> | information to checkpoint file. The small downside of doing this check
> | late is that we may have processed several processes in the tree before
> | hitting one that cannot be checkpointed.
> | 
> | We anyway walk the process tree we are checkpointing earlier, while
> | counting the tasks. We could check if all processes in the tree are
> | checkpointable at that time and fail early if any of them are not.
> | Since the process tree should be frozen, checking earlier should not
> | matter ?
> | 
> | For now, the patch leaves the existing check in cr_write_pids(). We
> | can remove that later.
> | 
> | Signed-off-by: Sukadev Bhattiprolu <sukadev-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>
> | ---
> |  checkpoint/checkpoint.c |    9 +++++++++
> |  1 files changed, 9 insertions(+), 0 deletions(-)
> | 
> | diff --git a/checkpoint/checkpoint.c b/checkpoint/checkpoint.c
> | index ed4fd3d..dae9b97 100644
> | --- a/checkpoint/checkpoint.c
> | +++ b/checkpoint/checkpoint.c
> | @@ -341,11 +341,18 @@ static int cr_tree_count_tasks(struct cr_ctx *ctx)
> |  	struct task_struct **tasks_arr = ctx->tasks_arr;
> |  	int tasks_nr = ctx->tasks_nr;
> |  	int nr = 0;
> | +	int ret;
> | 
> |  	read_lock(&tasklist_lock);
> | 
> |  	/* count tasks via DFS scan of the tree */
> |  	while (1) {
> | +		ret = cr_may_checkpoint_task(task, ctx);
> | +		if (ret < 0) {
> | +			nr = ret;
> | +			break;
> | +		}
> | +
> |  		if (tasks_arr) {
> |  			/* unlikely, but ... */
> |  			if (nr == tasks_nr)
> | @@ -401,6 +408,8 @@ static int cr_build_tree(struct cr_ctx *ctx)
> | 
> |  	/* count tasks (no side effects) */
> |  	n = cr_tree_count_tasks(ctx);
> | +	if (n < 0)
> | +		return n;

This hunk is already in v14.

-serge