Quoting Matt Helsley (matthltc@xxxxxxxxxx):
> Currently we allocate memory to output all of the epoll items in one
> big chunk. At 20 bytes per item, and since epoll was designed to
> support on the order of 10,000 items, we may find ourselves kmalloc'ing
> 200,000 bytes. That's an order 7 allocation whereas the heuristic for
> difficult allocations, PAGE_ALLOC_COST_ORDER, is 3.
>
> Instead, output the epoll header and items separately. Chunk the output
> much like the pid array gets chunked. This ensures that even sub-order 0
> allocations will enable checkpoint of large epoll sets. A subsequent
> patch will do something similar for the restore path.
>
> Signed-off-by: Matt Helsley <matthltc@xxxxxxxxxx>
Feels a bit auto-tune-magic-happy :) but looks good
Acked-by: Serge Hallyn <serue@xxxxxxxxxx>
> ---
> fs/eventpoll.c | 71 ++++++++++++++++++++++++++++++++++++-------------------
> 1 files changed, 46 insertions(+), 25 deletions(-)
>
> diff --git a/fs/eventpoll.c b/fs/eventpoll.c
> index 4706ec5..2506b40 100644
> --- a/fs/eventpoll.c
> +++ b/fs/eventpoll.c
> @@ -1480,7 +1480,7 @@ static int ep_items_checkpoint(void *data)
> struct rb_node *rbp;
> struct eventpoll *ep;
> __s32 epfile_objref;
> - int i, num_items, ret;
> + int num_items = 0, nchunk, ret;
>
> ctx = dq_entry->ctx;
>
> @@ -1489,9 +1489,8 @@ static int ep_items_checkpoint(void *data)
>
> ep = dq_entry->epfile->private_data;
> mutex_lock(&ep->mtx);
> - for (i = 0, rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp), i++) {}
> + for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp), num_items++) {}
> mutex_unlock(&ep->mtx);
> - num_items = i;
>
> h = ckpt_hdr_get_type(ctx, sizeof(*h), CKPT_HDR_EPOLL_ITEMS);
> if (!h)
> @@ -1503,36 +1502,58 @@ static int ep_items_checkpoint(void *data)
> if (ret || !num_items)
> return ret;
>
> - items = kzalloc(sizeof(*items)*num_items, GFP_KERNEL);
> + ret = ckpt_write_obj_type(ctx, NULL, sizeof(*items)*num_items,
> + CKPT_HDR_BUFFER);
> + if (ret < 0)
> + return ret;
> +
> + nchunk = num_items;
> + do {
> + items = kzalloc(sizeof(*items)*nchunk, GFP_KERNEL);
> + if (items)
> + break;
> + nchunk = nchunk >> 1;
> + } while (nchunk > 0);
> if (!items)
> return -ENOMEM;
> +
> + /*
> + * Walk the rbtree copying items into the chunk of memory and then
> + * writing them to the checkpoint image
> + */
> ret = 0;
> - i = 0;
> mutex_lock(&ep->mtx);
> - for (rbp = rb_first(&ep->rbr); i < num_items && rbp; rbp = rb_next(rbp),
> - i++) {
> - struct epitem *epi;
> - int objref;
> -
> - epi = rb_entry(rbp, struct epitem, rbn);
> - items[i].fd = epi->ffd.fd;
> - items[i].events = epi->event.events;
> - items[i].data = epi->event.data;
> - objref = ckpt_obj_lookup(ctx, epi->ffd.file, CKPT_OBJ_FILE);
> - if (objref <= 0) {
> - ret = -EBUSY; /* missing item -- checkpoint obj leak */
> - break;
> + rbp = rb_first(&ep->rbr);
> + while ((num_items > 0) && rbp) {
> + int n = min(num_items, nchunk);
> + int j;
> +
> + for (j = 0; rbp && j < n; j++, rbp = rb_next(rbp)) {
> + struct epitem *epi;
> + int objref;
> +
> + epi = rb_entry(rbp, struct epitem, rbn);
> + items[j].fd = epi->ffd.fd;
> + items[j].events = epi->event.events;
> + items[j].data = epi->event.data;
> + objref = ckpt_obj_lookup(ctx, epi->ffd.file,
> + CKPT_OBJ_FILE);
> + if (objref <= 0)
> + goto unlock;
> + items[j].file_objref = objref;
> }
> - items[i].file_objref = objref;
> + ret = ckpt_kwrite(ctx, items, n*sizeof(*items));
> + if (ret < 0)
> + break;
> + num_items -= n;
> }
> +unlock:
> mutex_unlock(&ep->mtx);
> - if (i == num_items && rbp)
> - ret = -EBUSY; /* extra item(s) -- checkpoint obj leak */
> - if (!ret)
> - ret = ckpt_write_buffer(ctx, items, sizeof(*items)*num_items);
> - else
> - ckpt_write_err(ctx, "E", "checkpoint leak detected.\n", ret);
> kfree(items);
> + if (num_items != 0 || (num_items == 0 && rbp))
> + ret = -EBUSY; /* extra item(s) -- checkpoint obj leak */
> + if (ret)
> + ckpt_write_err(ctx, "E", " checkpointing epoll items.\n", ret);
> return ret;
> }
>
> --
> 1.5.6.3
>
>
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