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SUNRPC: Optimize rq_respages allocation in svc_alloc_arg

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svc_alloc_arg() invokes alloc_pages_bulk() with the full rq_maxpages
count (~259 for 1MB messages) for the rq_respages array, causing a
full-array scan despite most slots holding valid pages.

svc_rqst_release_pages() NULLs only the range

  [rq_respages, rq_next_page)

after each RPC, so only that range contains NULL entries. Limit the
rq_respages fill in svc_alloc_arg() to that range instead of
scanning the full array.

svc_init_buffer() initializes rq_next_page to span the entire
rq_respages array, so the first svc_alloc_arg() call fills all
slots.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
This commit is contained in:
Chuck Lever
2026-02-26 09:47:39 -05:00
parent 7ed7504287
commit d7f3efd9ff
3 changed files with 12 additions and 1 deletions
Download Patch File Download Diff File Expand all files Collapse all files

4
include/linux/sunrpc/svc.h
View File

@@ -152,6 +152,10 @@ extern u32 svc_max_payload(const struct svc_rqst *rqstp);
* still in transport use, and set rq_pages_nfree to the count.
* svc_alloc_arg() refills only that many rq_pages entries.
*
* For rq_respages, svc_rqst_release_pages() NULLs entries in
* [rq_respages, rq_next_page) after each RPC. svc_alloc_arg()
* refills only that range.
*
* xdr_buf holds responses; the structure fits NFS read responses
* (header, data pages, optional tail) and enables sharing of
* client-side routines.

1
net/sunrpc/svc.c
View File

@@ -656,6 +656,7 @@ svc_init_buffer(struct svc_rqst *rqstp, const struct svc_serv *serv, int node)
}
rqstp->rq_pages_nfree = rqstp->rq_maxpages;
rqstp->rq_next_page = rqstp->rq_respages + rqstp->rq_maxpages;
return true;
}

8
net/sunrpc/svc_xprt.c
View File

@@ -686,8 +686,14 @@ static bool svc_alloc_arg(struct svc_rqst *rqstp)
rqstp->rq_pages_nfree = 0;
}
if (!svc_fill_pages(rqstp, rqstp->rq_respages, pages))
if (WARN_ON_ONCE(rqstp->rq_next_page < rqstp->rq_respages))
return false;
nfree = rqstp->rq_next_page - rqstp->rq_respages;
if (nfree) {
if (!svc_fill_pages(rqstp, rqstp->rq_respages, nfree))
return false;
}
rqstp->rq_next_page = rqstp->rq_respages;
rqstp->rq_page_end = &rqstp->rq_respages[pages];
/* svc_rqst_replace_page() dereferences *rq_next_page even