From: Chuck Lever <chuck.lever@xxxxxxxxxx>
Subject: SUNRPC: set rq_page_end differently
Patch series "SUNRPC consumer for the bulk page allocator"
This patch set and the measurements below are based on yesterday's
bulk allocator series:
git://git.kernel.org/pub/scm/linux/kernel/git/mel/linux.git mm-bulk-rebase-v5r9
The patches change SUNRPC to invoke the array-based bulk allocator
instead of alloc_page().
The micro-benchmark results are promising. I ran a mixture of 256KB
reads and writes over NFSv3. The server's kernel is built with KASAN
enabled, so the comparison is exaggerated but I believe it is still
valid.
I instrumented svc_recv() to measure the latency of each call to
svc_alloc_arg() and report it via a trace point. The following
results are averages across the trace events.
Single page: 25.007 us per call over 532,571 calls
Bulk list: 6.258 us per call over 517,034 calls
Bulk array: 4.590 us per call over 517,442 calls
This patch (of 2)
Refactor:
I'm about to use the loop variable @i for something else.
As far as the "i++" is concerned, that is a post-increment. The
value of @i is not used subsequently, so the increment operator
is unnecessary and can be removed.
Also note that nfsd_read_actor() was renamed nfsd_splice_actor()
by commit cf8208d0eabd ("sendfile: convert nfsd to
splice_direct_to_actor()").
Link: https://lkml.kernel.org/r/20210325114228.27719-7-mgorman@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Reviewed-by: Alexander Lobakin <alobakin@xxxxx>
Cc: Alexander Duyck <alexander.duyck@xxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: David Miller <davem@xxxxxxxxxxxxx>
Cc: Ilias Apalodimas <ilias.apalodimas@xxxxxxxxxx>
Cc: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
net/sunrpc/svc_xprt.c | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)
--- a/net/sunrpc/svc_xprt.c~sunrpc-set-rq_page_end-differently
+++ a/net/sunrpc/svc_xprt.c
@@ -661,7 +661,7 @@ static void svc_check_conn_limits(struct
static int svc_alloc_arg(struct svc_rqst *rqstp)
{
struct svc_serv *serv = rqstp->rq_server;
- struct xdr_buf *arg;
+ struct xdr_buf *arg = &rqstp->rq_arg;
int pages;
int i;
@@ -686,11 +686,10 @@ static int svc_alloc_arg(struct svc_rqst
}
rqstp->rq_pages[i] = p;
}
- rqstp->rq_page_end = &rqstp->rq_pages[i];
- rqstp->rq_pages[i++] = NULL; /* this might be seen in nfs_read_actor */
+ rqstp->rq_page_end = &rqstp->rq_pages[pages];
+ rqstp->rq_pages[pages] = NULL; /* this might be seen in nfsd_splice_actor() */
/* Make arg->head point to first page and arg->pages point to rest */
- arg = &rqstp->rq_arg;
arg->head[0].iov_base = page_address(rqstp->rq_pages[0]);
arg->head[0].iov_len = PAGE_SIZE;
arg->pages = rqstp->rq_pages + 1;
_
