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svcrdma: Avoid releasing a page in svc_xprt_release()

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svc_xprt_release() invokes svc_free_res_pages(), which releases
pages between rq_respages and rq_next_page.

Historically, the RPC/RDMA transport has set these two pointers to
be different by one, which means:

- one page gets released when svc_recv returns 0. This normally
happens whenever one or more RDMA Reads need to be dispatched to
complete construction of an RPC Call.

- one page gets released after every call to svc_send.

In both cases, this released page is immediately refilled by
svc_alloc_arg. There does not seem to be a reason for releasing this
page.

To avoid this unnecessary memory allocator traffic, set rq_next_page
more carefully.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
This commit is contained in:
Chuck Lever 2018-07-27 11:18:54 -04:00 committed by J. Bruce Fields
parent 7b4d6da4bb
commit a53d5cb064
2 changed files with 9 additions and 4 deletions
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9
net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
View File

@ -366,9 +366,6 @@ static void svc_rdma_build_arg_xdr(struct svc_rqst *rqstp,
arg->page_base = 0;
arg->buflen = ctxt->rc_byte_len;
arg->len = ctxt->rc_byte_len;
rqstp->rq_respages = &rqstp->rq_pages[0];
rqstp->rq_next_page = rqstp->rq_respages + 1;
}
/* This accommodates the largest possible Write chunk,
@ -730,6 +727,12 @@ int svc_rdma_recvfrom(struct svc_rqst *rqstp)
svc_rdma_build_arg_xdr(rqstp, ctxt);
/* Prevent svc_xprt_release from releasing pages in rq_pages
* if we return 0 or an error.
*/
rqstp->rq_respages = rqstp->rq_pages;
rqstp->rq_next_page = rqstp->rq_respages;
p = (__be32 *)rqstp->rq_arg.head[0].iov_base;
ret = svc_rdma_xdr_decode_req(&rqstp->rq_arg);
if (ret < 0)

4
net/sunrpc/xprtrdma/svc_rdma_sendto.c
View File

@ -657,7 +657,9 @@ static void svc_rdma_save_io_pages(struct svc_rqst *rqstp,
ctxt->sc_pages[i] = rqstp->rq_respages[i];
rqstp->rq_respages[i] = NULL;
}
rqstp->rq_next_page = rqstp->rq_respages + 1;
/* Prevent svc_xprt_release from releasing pages in rq_pages */
rqstp->rq_next_page = rqstp->rq_respages;
}
/* Prepare the portion of the RPC Reply that will be transmitted