[PATCH v4 04/14] sunrpc: Replace the rq_pages array with dynamically-allocated memory

cel
2025-04-28T19:37:10Z

From: Chuck Lever <chuck.lever@oracle.com>

As a step towards making NFSD's maximum rsize and wsize variable at
run-time, replace the fixed-size rq_vec[] array in struct svc_rqst
with a chunk of dynamically-allocated memory.

On a system with 8-byte pointers and 4KB pages, pahole reports that
the rq_pages[] array is 2080 bytes. This patch replaces that with
a single 8-byte pointer field.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
include/linux/sunrpc/svc.h | 3 ++-
net/sunrpc/svc.c | 34 ++++++++++++++++++-------------
net/sunrpc/svc_xprt.c | 10 +--------
net/sunrpc/xprtrdma/svc_rdma_rw.c | 2 +-
4 files changed, 24 insertions(+), 25 deletions(-)

diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
index e83ac14267e8..ea3a33eec29b 100644
--- a/include/linux/sunrpc/svc.h
+++ b/include/linux/sunrpc/svc.h
@@ -205,7 +205,8 @@ struct svc_rqst {
struct xdr_stream rq_res_stream;
struct page *rq_scratch_page;
struct xdr_buf rq_res;
- struct page *rq_pages[RPCSVC_MAXPAGES + 1];
+ unsigned long rq_maxpages; /* num of entries in rq_pages */
+ struct page * *rq_pages;
struct page * *rq_respages; /* points into rq_pages */
struct page * *rq_next_page; /* next reply page to use */
struct page * *rq_page_end; /* one past the last page */
diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index 8ce3e6b3df6a..682e11c9be36 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -636,20 +636,25 @@ svc_destroy(struct svc_serv **servp)
EXPORT_SYMBOL_GPL(svc_destroy);

static bool
-svc_init_buffer(struct svc_rqst *rqstp, unsigned int size, int node)
+svc_init_buffer(struct svc_rqst *rqstp, const struct svc_serv *serv, int node)
{
- unsigned long pages, ret;
+ unsigned long ret;

- pages = size / PAGE_SIZE + 1; /* extra page as we hold both request and reply.
- * We assume one is at most one page
- */
- WARN_ON_ONCE(pages > RPCSVC_MAXPAGES);
- if (pages > RPCSVC_MAXPAGES)
- pages = RPCSVC_MAXPAGES;
+ /* Add an extra page, as rq_pages holds both request and reply.
+ * We assume one of those is at most one page.
+ */
+ rqstp->rq_maxpages = svc_serv_maxpages(serv) + 1;

- ret = alloc_pages_bulk_node(GFP_KERNEL, node, pages,
+ /* rq_pages' last entry is NULL for historical reasons. */
+ rqstp->rq_pages = kcalloc_node(rqstp->rq_maxpages + 1,
+ sizeof(struct page *),
+ GFP_KERNEL, node);
+ if (!rqstp->rq_pages)
+ return false;
+
+ ret = alloc_pages_bulk_node(GFP_KERNEL, node, rqstp->rq_maxpages,
rqstp->rq_pages);
- return ret == pages;
+ return ret == rqstp->rq_maxpages;
}

/*
@@ -658,11 +663,12 @@ svc_init_buffer(struct svc_rqst *rqstp, unsigned int size, int node)
static void
svc_release_buffer(struct svc_rqst *rqstp)
{
- unsigned int i;
+ unsigned long i;

- for (i = 0; i < ARRAY_SIZE(rqstp->rq_pages); i++)
+ for (i = 0; i < rqstp->rq_maxpages; i++)
if (rqstp->rq_pages[i])
put_page(rqstp->rq_pages[i]);
+ kfree(rqstp->rq_pages);
}

static void
@@ -704,7 +710,7 @@ svc_prepare_thread(struct svc_serv *serv, struct svc_pool *pool, int node)
if (!rqstp->rq_resp)
goto out_enomem;

- if (!svc_init_buffer(rqstp, serv->sv_max_mesg, node))
+ if (!svc_init_buffer(rqstp, serv, node))
goto out_enomem;

rqstp->rq_err = -EAGAIN; /* No error yet */
@@ -896,7 +902,7 @@ EXPORT_SYMBOL_GPL(svc_set_num_threads);
bool svc_rqst_replace_page(struct svc_rqst *rqstp, struct page *page)
{
struct page **begin = rqstp->rq_pages;
- struct page **end = &rqstp->rq_pages[RPCSVC_MAXPAGES];
+ struct page **end = &rqstp->rq_pages[rqstp->rq_maxpages];

if (unlikely(rqstp->rq_next_page < begin || rqstp->rq_next_page > end)) {
trace_svc_replace_page_err(rqstp);
diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index ae25405d8bd2..23547ed25269 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -651,18 +651,10 @@ static void svc_check_conn_limits(struct svc_serv *serv)

static bool svc_alloc_arg(struct svc_rqst *rqstp)
{
- struct svc_serv *serv = rqstp->rq_server;
struct xdr_buf *arg = &rqstp->rq_arg;
unsigned long pages, filled, ret;

- pages = (serv->sv_max_mesg + 2 * PAGE_SIZE) >> PAGE_SHIFT;
- if (pages > RPCSVC_MAXPAGES) {
- pr_warn_once("svc: warning: pages=%lu > RPCSVC_MAXPAGES=%lu\n",
- pages, RPCSVC_MAXPAGES);
- /* use as many pages as possible */
- pages = RPCSVC_MAXPAGES;
- }
-
+ pages = rqstp->rq_maxpages;
for (filled = 0; filled < pages; filled = ret) {
ret = alloc_pages_bulk(GFP_KERNEL, pages, rqstp->rq_pages);
if (ret > filled)
diff --git a/net/sunrpc/xprtrdma/svc_rdma_rw.c b/net/sunrpc/xprtrdma/svc_rdma_rw.c
index 40797114d50a..661b3fe2779f 100644
--- a/net/sunrpc/xprtrdma/svc_rdma_rw.c
+++ b/net/sunrpc/xprtrdma/svc_rdma_rw.c
@@ -765,7 +765,7 @@ static int svc_rdma_build_read_segment(struct svc_rqst *rqstp,
}
len -= seg_len;

- if (len && ((head->rc_curpage + 1) > ARRAY_SIZE(rqstp->rq_pages)))
+ if (len && ((head->rc_curpage + 1) > rqstp->rq_maxpages))
goto out_overrun;
}

--
2.49.0