From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 55A2F37524F for ; Sat, 28 Feb 2026 18:16:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772302603; cv=none; b=MyGKUxlwK4sUoyXRreFDf1Y5aIaWLBjrkgi3fsIu1nufEcWTgAT8rkU5CprQ78hIIoh6LgrUrFrfQS9lXTBbZ2f4frr2FK0DmMExguz/SinITVJNu05fx7FaMn+PpC9TyVrzHilrtIRkZkEuSFVkQRsfHEJR7E2UqOfuOfJxNAY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772302603; c=relaxed/simple; bh=p8tzr+aJj8k5+Xsu4N9v0bIRJ2qztcnep0+aIcYXLks=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=SG+EiaiW61Daan5Ihk8MTp/sbGY4VzRNox5B8TtdnS/lHOMsHU3s5fPYmBbRvgxJnoOhS1caF7+NoPXtUY45Z5JZnaodmM3plcWhW56B1x3vOSl++XBYodCiQD9x1jvBxfTwXx2oalRKEvWJgHdbTOAuXJOuE+GuTt1LcQnObUA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=DYuYbL10; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="DYuYbL10" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D09BBC19423; Sat, 28 Feb 2026 18:16:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772302603; bh=p8tzr+aJj8k5+Xsu4N9v0bIRJ2qztcnep0+aIcYXLks=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=DYuYbL10k9vFPJn0x8x8+LLuEIxzrvawvIzQz5gUAtM7dELwPwX5Igr1doeBAEdBZ bjLVtiFVVDU1I0jpSDSoXxqDA99w2lIMSEfEv/leykiBJZ7FnMVPW79PTgPuN/36rK ryjnAzw/wD3nB4JEP4jDyYORBWTtSfRE2mfGPbo4q18uqOY7uX42YYGHH1SFU/i89i 8KYk/2jQD3BT55C20LCAOfwgTExe+fB/YgCgpAK48XYdmJXyxLdnnZWbXfrBP4w9b0 kqQT9xn9xK5/lTogDwKBkj1XI2fvzL9mKjMWO4k6Rk4s+8FJG0dbpSArBSUsNmpa0Y wbxNLYuQxiZhg== From: Sasha Levin To: patches@lists.linux.dev Cc: Chuck Lever , Sasha Levin Subject: [PATCH 5.15 117/164] svcrdma: Increase the per-transport rw_ctx count Date: Sat, 28 Feb 2026 13:14:16 -0500 Message-ID: <20260228181505.1600663-117-sashal@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260228181505.1600663-1-sashal@kernel.org> References: <20260228181505.1600663-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit From: Chuck Lever [ Upstream commit 2da0f610e733606e06284ac3c1f188b9dec75d68 ] rdma_rw_mr_factor() returns the smallest number of MRs needed to move a particular number of pages. svcrdma currently asks for the number of MRs needed to move RPCSVC_MAXPAGES (a little over one megabyte), as that is the number of pages in the largest r/wsize the server supports. This call assumes that the client's NIC can bundle a full one megabyte payload in a single rdma_segment. In fact, most NICs cannot handle a full megabyte with a single rkey / rdma_segment. Clients will typically split even a single Read chunk into many segments. The server needs one MR to read each rdma_segment in a Read chunk, and thus each one needs an rw_ctx. svcrdma has been vastly underestimating the number of rw_ctxs needed to handle 64 RPC requests with large Read chunks using small rdma_segments. Unfortunately there doesn't seem to be a good way to estimate this number without knowing the client NIC's capabilities. Even then, the client RPC/RDMA implementation is still free to split a chunk into smaller segments (for example, it might be using physical registration, which needs an rdma_segment per page). The best we can do for now is choose a number that will guarantee forward progress in the worst case (one page per segment). At some later point, we could add some mechanisms to make this much less of a problem: - Add a core API to add more rw_ctxs to an already-established QP - svcrdma could treat rw_ctx exhaustion as a temporary error and try again - Limit the number of Reads in flight Signed-off-by: Chuck Lever Stable-dep-of: afcae7d7b8a2 ("RDMA/core: add rdma_rw_max_sge() helper for SQ sizing") Signed-off-by: Sasha Levin --- net/sunrpc/xprtrdma/svc_rdma_transport.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/net/sunrpc/xprtrdma/svc_rdma_transport.c b/net/sunrpc/xprtrdma/svc_rdma_transport.c index 31e6f4a14bbc0..3d3b15f9d6d51 100644 --- a/net/sunrpc/xprtrdma/svc_rdma_transport.c +++ b/net/sunrpc/xprtrdma/svc_rdma_transport.c @@ -417,8 +417,13 @@ static struct svc_xprt *svc_rdma_accept(struct svc_xprt *xprt) newxprt->sc_max_requests = rq_depth - 2; newxprt->sc_max_bc_requests = 2; } - ctxts = rdma_rw_mr_factor(dev, newxprt->sc_port_num, RPCSVC_MAXPAGES); - ctxts *= newxprt->sc_max_requests; + + /* Arbitrarily estimate the number of rw_ctxs needed for + * this transport. This is enough rw_ctxs to make forward + * progress even if the client is using one rkey per page + * in each Read chunk. + */ + ctxts = 3 * RPCSVC_MAXPAGES; newxprt->sc_sq_depth = rq_depth + ctxts; if (newxprt->sc_sq_depth > dev->attrs.max_qp_wr) newxprt->sc_sq_depth = dev->attrs.max_qp_wr; -- 2.51.0