On Wed, 29 Feb 2012, Alex Elder wrote:
> Each messenger allocates a page to be used when writing zeroes
> out in the event of error or other abnormal condition. Instead,
> use the kernel ZERO_PAGE() for that purpose.
>
> Signed-off-by: Alex Elder <elder@xxxxxxxxxxxxx>
> ---
> v2: Updated to use kernel ZERO_PAGE()
>
> include/linux/ceph/messenger.h | 1
> net/ceph/messenger.c | 43
> +++++++++++++++++++++++++++--------------
> 2 files changed, 29 insertions(+), 15 deletions(-)
>
> Index: b/include/linux/ceph/messenger.h
> ===================================================================
> --- a/include/linux/ceph/messenger.h
> +++ b/include/linux/ceph/messenger.h
> @@ -54,7 +54,6 @@ struct ceph_connection_operations {
> struct ceph_messenger {
> struct ceph_entity_inst inst; /* my name+address */
> struct ceph_entity_addr my_enc_addr;
> - struct page *zero_page; /* used in certain error cases */
>
> bool nocrc;
>
> Index: b/net/ceph/messenger.c
> ===================================================================
> --- a/net/ceph/messenger.c
> +++ b/net/ceph/messenger.c
> @@ -52,6 +52,9 @@ static char addr_str[MAX_ADDR_STR][MAX_A
> static DEFINE_SPINLOCK(addr_str_lock);
> static int last_addr_str;
>
> +static struct page *zero_page; /* used in certain error cases */
> +static void *zero_page_address; /* kernel virtual addr of
> zero_page */
> +
> const char *ceph_pr_addr(const struct sockaddr_storage *ss)
> {
> int i;
> @@ -99,18 +102,41 @@ struct workqueue_struct *ceph_msgr_wq;
>
> int ceph_msgr_init(void)
> {
> + BUG_ON(zero_page != NULL);
> + zero_page = ZERO_PAGE(0);
> + page_cache_get(zero_page);
> +
> + BUG_ON(zero_page_address != NULL);
> + zero_page_address = kmap(zero_page);
I've always assumed that kmap() used up an expensive slot, and that pages
should be kmapped only when needed. Myabe this should still be done
inside write_partial_msg_pages()?
> +
> ceph_msgr_wq = alloc_workqueue("ceph-msgr", WQ_NON_REENTRANT, 0);
> if (!ceph_msgr_wq) {
> pr_err("msgr_init failed to create workqueue\n");
> +
> + zero_page_address = NULL;
> + kunmap(zero_page);
> + page_cache_release(zero_page);
> + zero_page = NULL;
> +
> return -ENOMEM;
> }
> +
> return 0;
> }
> EXPORT_SYMBOL(ceph_msgr_init);
>
> void ceph_msgr_exit(void)
> {
> + BUG_ON(ceph_msgr_wq == NULL);
> destroy_workqueue(ceph_msgr_wq);
> +
> + BUG_ON(zero_page_address == NULL);
> + zero_page_address = NULL;
> +
> + BUG_ON(zero_page == NULL);
> + kunmap(zero_page);
> + page_cache_release(zero_page);
> + zero_page = NULL;
> }
> EXPORT_SYMBOL(ceph_msgr_exit);
>
> @@ -841,9 +867,9 @@ static int write_partial_msg_pages(struc
> max_write = bv->bv_len;
> #endif
> } else {
> - page = con->msgr->zero_page;
> + page = zero_page;
> if (crc)
> - kaddr = page_address(con->msgr->zero_page);
> + kaddr = zero_page_address;
> }
> len = min_t(int, max_write - con->out_msg_pos.page_pos,
> total_max_write);
> @@ -914,7 +940,7 @@ static int write_partial_skip(struct cep
>
> while (con->out_skip > 0) {
> struct kvec iov = {
> - .iov_base = page_address(con->msgr->zero_page),
> + .iov_base = zero_page_address,
> .iov_len = min(con->out_skip, (int)PAGE_CACHE_SIZE)
> };
>
> @@ -2222,15 +2248,6 @@ struct ceph_messenger *ceph_messenger_cr
>
> spin_lock_init(&msgr->global_seq_lock);
>
> - /* the zero page is needed if a request is "canceled" while the
> message
> - * is being written over the socket */
> - msgr->zero_page = __page_cache_alloc(GFP_KERNEL | __GFP_ZERO);
> - if (!msgr->zero_page) {
> - kfree(msgr);
> - return ERR_PTR(-ENOMEM);
> - }
> - kmap(msgr->zero_page);
> -
> if (myaddr)
> msgr->inst.addr = *myaddr;
>
> @@ -2247,8 +2264,6 @@ EXPORT_SYMBOL(ceph_messenger_create);
> void ceph_messenger_destroy(struct ceph_messenger *msgr)
> {
> dout("destroy %p\n", msgr);
> - kunmap(msgr->zero_page);
> - __free_page(msgr->zero_page);
> kfree(msgr);
> dout("destroyed messenger %p\n", msgr);
> }
>
> --
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