From ab8362645fba90fa44ec1991ad05544e307dd02f Mon Sep 17 00:00:00 2001 From: Chuck Lever Date: Thu, 29 Apr 2021 23:01:58 -0700 Subject: [PATCH] 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@techsingularity.net Signed-off-by: Chuck Lever Signed-off-by: Mel Gorman Reviewed-by: Alexander Lobakin Cc: Alexander Duyck Cc: Christoph Hellwig Cc: David Miller Cc: Ilias Apalodimas Cc: Jesper Dangaard Brouer Cc: Matthew Wilcox (Oracle) Cc: Vlastimil Babka Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- net/sunrpc/svc_xprt.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c index 42565f0..63eb6b9a 100644 --- a/net/sunrpc/svc_xprt.c +++ b/net/sunrpc/svc_xprt.c @@ -661,7 +661,7 @@ static void svc_check_conn_limits(struct svc_serv *serv) 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) } 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; -- 2.7.4