Re: [PATCH 3/3] epoll: Add support for restoring many epoll items

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

Quoting Matt Helsley (matthltc-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org):
> This completes the work necessary to make checkpoint/restart of
> thousands of epoll items more reliable when higher order kmallocs
> would fail. We grab a piece of memory suitable to store a "chunk"
> of items for input. Read the input one chunk at a time and add
> epoll items for each item in the chunk.
> 
> Signed-off-by: Matt Helsley <matthltc-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>

Acked-by: Serge Hallyn <serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>

> ---
>  fs/eventpoll.c |   58 +++++++++++++++++++++++++++++++++++--------------------
>  1 files changed, 37 insertions(+), 21 deletions(-)
> 
> diff --git a/fs/eventpoll.c b/fs/eventpoll.c
> index 2506b40..c261263 100644
> --- a/fs/eventpoll.c
> +++ b/fs/eventpoll.c
> @@ -1594,7 +1594,7 @@ static int ep_items_restore(void *data)
>  	struct ckpt_eventpoll_item *items = NULL;
>  	struct eventpoll *ep;
>  	struct file *epfile = NULL;
> -	int ret, num_items, i = 0;
> +	int ret, num_items, nchunk;
> 
>  	h = ckpt_read_obj_type(ctx, sizeof(*h), CKPT_HDR_EPOLL_ITEMS);
>  	if (IS_ERR(h))
> @@ -1611,34 +1611,50 @@ static int ep_items_restore(void *data)
>  	if (!num_items)
>  		return 0;
> 
> -	ret = ckpt_read_payload(ctx, (void**)&items, num_items*sizeof(*items),
> -				CKPT_HDR_BUFFER);
> +	ret = _ckpt_read_obj_type(ctx, NULL, 0, CKPT_HDR_BUFFER);
> +	if (ret < 0)
> +		return ret;
> +	/* Make sure the items match the size we expect */
> +	if (num_items != (ret / sizeof(*items)))
> +		return -EINVAL;
> +
> +	nchunk = num_items;
> +	do {
> +		items = kzalloc(sizeof(*items)*nchunk, GFP_KERNEL);
> +		if (items)
> +			break;
> +		nchunk = nchunk/2;
> +	} while (nchunk > 0);
>  	if (!items)
>  		return -ENOMEM;
> 
> -	/* Make sure the items match the size we expect */
> -	if (num_items != (ret / sizeof(*items))) {
> -		ret = -EINVAL;
> -		goto out;
> -	}
> -
>  	ep = epfile->private_data;
> 
> -	/* Restore the epoll items/watches */
> -	for (ret = 0, i = 0; !ret && i < num_items; i++) {
> -		struct epoll_event epev;
> -		struct file *tfile;
> +	while (num_items > 0) {
> +		int n = min(num_items, nchunk);
> +		int j;
> 
> -		tfile = ckpt_obj_fetch(ctx, items[i].file_objref,
> -				       CKPT_OBJ_FILE);
> -		if (IS_ERR(tfile)) {
> -			ret = PTR_ERR(tfile);
> +		ret = ckpt_kread(ctx, items, n*sizeof(*items));
> +		if (ret < 0)
>  			break;
> +
> +		/* Restore the epoll items/watches */
> +		for (j = 0; !ret && j < n; j++) {
> +			struct epoll_event epev;
> +			struct file *tfile;
> +
> +			tfile = ckpt_obj_fetch(ctx, items[j].file_objref,
> +					       CKPT_OBJ_FILE);
> +			if (IS_ERR(tfile)) {
> +				ret = PTR_ERR(tfile);
> +				goto out;
> +			}
> +			epev.events = items[j].events;
> +			epev.data = items[j].data;
> +			ret = do_epoll_ctl(EPOLL_CTL_ADD, items[j].fd,
> +					   epfile, tfile, &epev);
>  		}
> -		epev.events = items[i].events;
> -		epev.data = items[i].data;
> -		ret = do_epoll_ctl(EPOLL_CTL_ADD, items[i].fd,
> -				   epfile, tfile, &epev);
> +		num_items -= n;
>  	}
>  out:
>  	kfree(items);
> -- 
> 1.5.6.3
> 
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