On Mon, Feb 22 2021, Chuck Lever wrote:
> To avoid extra trips to the page allocator, don't free unused pages
> in nfsd_splice_actor(), but instead place them in a local cache.
> That cache is then used first when refilling rq_pages.
>
> On workloads that perform large NFS READs on splice-capable file
> systems, this saves a considerable amount of work.
>
> Suggested-by: NeilBrown <neilb@xxxxxxx>
> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
> ---
> fs/nfsd/vfs.c | 4 ++--
> include/linux/sunrpc/svc.h | 1 +
> include/linux/sunrpc/svc_xprt.h | 28 ++++++++++++++++++++++++++++
> net/sunrpc/svc.c | 7 +++++++
> net/sunrpc/svc_xprt.c | 12 ++++++++++++
> 5 files changed, 50 insertions(+), 2 deletions(-)
>
> diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
> index d316e11923c5..25cf41eaf3c4 100644
> --- a/fs/nfsd/vfs.c
> +++ b/fs/nfsd/vfs.c
> @@ -852,14 +852,14 @@ nfsd_splice_actor(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
>
> if (rqstp->rq_res.page_len == 0) {
> get_page(page);
> - put_page(*rqstp->rq_next_page);
> + svc_rqst_put_unused_page(rqstp, *rqstp->rq_next_page);
> *(rqstp->rq_next_page++) = page;
> rqstp->rq_res.page_base = buf->offset;
> rqstp->rq_res.page_len = size;
> } else if (page != pp[-1]) {
> get_page(page);
> if (*rqstp->rq_next_page)
> - put_page(*rqstp->rq_next_page);
> + svc_rqst_put_unused_page(rqstp, *rqstp->rq_next_page);
> *(rqstp->rq_next_page++) = page;
> rqstp->rq_res.page_len += size;
> } else
> diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
> index 31ee3b6047c3..340f4f3989c0 100644
> --- a/include/linux/sunrpc/svc.h
> +++ b/include/linux/sunrpc/svc.h
> @@ -250,6 +250,7 @@ struct svc_rqst {
> struct xdr_stream rq_arg_stream;
> struct page *rq_scratch_page;
> struct xdr_buf rq_res;
> + struct list_head rq_unused_pages;
> struct page *rq_pages[RPCSVC_MAXPAGES + 1];
> struct page * *rq_respages; /* points into rq_pages */
> struct page * *rq_next_page; /* next reply page to use */
> diff --git a/include/linux/sunrpc/svc_xprt.h b/include/linux/sunrpc/svc_xprt.h
> index 571f605bc91e..49ef86499876 100644
> --- a/include/linux/sunrpc/svc_xprt.h
> +++ b/include/linux/sunrpc/svc_xprt.h
> @@ -150,6 +150,34 @@ static inline void svc_xprt_get(struct svc_xprt *xprt)
> {
> kref_get(&xprt->xpt_ref);
> }
> +
> +/**
> + * svc_rqst_get_unused_page - Tap a page from the local cache
> + * @rqstp: svc_rqst with cached unused pages
> + *
> + * To save an allocator round trip, pages can be added to a
> + * local cache and re-used later by svc_alloc_arg().
> + *
> + * Returns an unused page, or NULL if the cache is empty.
> + */
> +static inline struct page *svc_rqst_get_unused_page(struct svc_rqst *rqstp)
> +{
> + return list_first_entry_or_null(&rqstp->rq_unused_pages,
> + struct page, lru);
> +}
> +
> +/**
> + * svc_rqst_put_unused_page - Stash a page in the local cache
> + * @rqstp: svc_rqst with cached unused pages
> + * @page: page to cache
> + *
> + */
> +static inline void svc_rqst_put_unused_page(struct svc_rqst *rqstp,
> + struct page *page)
> +{
> + list_add(&page->lru, &rqstp->rq_unused_pages);
> +}
> +
> static inline void svc_xprt_set_local(struct svc_xprt *xprt,
> const struct sockaddr *sa,
> const size_t salen)
> diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
> index 61fb8a18552c..3920fa8f1146 100644
> --- a/net/sunrpc/svc.c
> +++ b/net/sunrpc/svc.c
> @@ -570,6 +570,8 @@ svc_init_buffer(struct svc_rqst *rqstp, unsigned int size, int node)
> if (svc_is_backchannel(rqstp))
> return 1;
>
> + INIT_LIST_HEAD(&rqstp->rq_unused_pages);
> +
> pages = size / PAGE_SIZE + 1; /* extra page as we hold both request and reply.
> * We assume one is at most one page
> */
> @@ -593,8 +595,13 @@ svc_init_buffer(struct svc_rqst *rqstp, unsigned int size, int node)
> static void
> svc_release_buffer(struct svc_rqst *rqstp)
> {
> + struct page *page;
> unsigned int i;
>
> + while ((page = svc_rqst_get_unused_page(rqstp))) {
> + list_del(&page->lru);
> + put_page(page);
> + }
> for (i = 0; i < ARRAY_SIZE(rqstp->rq_pages); i++)
> if (rqstp->rq_pages[i])
> put_page(rqstp->rq_pages[i]);
> diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
> index 15aacfa5ca21..84210e546a66 100644
> --- a/net/sunrpc/svc_xprt.c
> +++ b/net/sunrpc/svc_xprt.c
> @@ -678,6 +678,18 @@ static int svc_alloc_arg(struct svc_rqst *rqstp)
> for (needed = 0, i = 0; i < pages ; i++)
> if (!rqstp->rq_pages[i])
> needed++;
> + if (needed) {
> + for (i = 0; i < pages; i++) {
> + if (!rqstp->rq_pages[i]) {
> + page = svc_rqst_get_unused_page(rqstp);
> + if (!page)
> + break;
> + list_del(&page->lru);
> + rqstp->rq_pages[i] = page;
> + needed--;
> + }
> + }
> + }
> if (needed) {
> LIST_HEAD(list);
>
This looks good! Probably simpler than the way I imagined it :-)
I would do that last bit of code differently though...
for (needed = 0, i = 0; i < pages ; i++)
if (!rqstp->rq_pages[i]) {
page = svc_rqst_get_unused_pages(rqstp);
if (page) {
list_del(&page->lru);
rqstp->rq_pages[i] = page;
} else
needed++;
}
but it is really a minor style difference - I don't object to your
version.
Reviewed-by: NeilBrown <neilb@xxxxxxx>
Thanks,
NeilBrown
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