From patchwork Mon Nov 21 13:35:17 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Benjamin Coddington X-Patchwork-Id: 13050923 X-Patchwork-Delegate: kuba@kernel.org Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6E4FEC43219 for ; Mon, 21 Nov 2022 13:36:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231229AbiKUNgt (ORCPT ); Mon, 21 Nov 2022 08:36:49 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41760 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231195AbiKUNgj (ORCPT ); Mon, 21 Nov 2022 08:36:39 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0D794C2854 for ; Mon, 21 Nov 2022 05:35:38 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1669037737; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=1lfaZmEr1+sFIs7mldxdSC2PRz/TSl8NkLASLsIdT4M=; b=Uw9bNaqJ0cYiuj5GLjWRuf1ffv8rRCZZhVFCrbSC1+cvmZNBXAfjR6ZmNKo60K3mLjcG9B h/dY9FS/rTWpFtQdIeSaW82WJ6xecooFhynx//TYr9gFf0vOQdtsmMBbyJgwZ6PxbiZuSA btv//SMrzZf2DPZ7imuMnuzZ5q7a9hQ= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-488-JtJ1gjWcOKWJCL_6qFNyuQ-1; Mon, 21 Nov 2022 08:35:34 -0500 X-MC-Unique: JtJ1gjWcOKWJCL_6qFNyuQ-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id A1F5E3C10144; Mon, 21 Nov 2022 13:35:33 +0000 (UTC) Received: from bcodding.csb (unknown [10.22.50.7]) by smtp.corp.redhat.com (Postfix) with ESMTP id 1B663492B06; Mon, 21 Nov 2022 13:35:33 +0000 (UTC) Received: by bcodding.csb (Postfix, from userid 24008) id ABC5C10C30E3; Mon, 21 Nov 2022 08:35:30 -0500 (EST) From: Benjamin Coddington To: netdev@vger.kernel.org Cc: linux-kernel@vger.kernel.org, "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Soheil Hassas Yeganeh , Shakeel Butt , Pavel Begunkov , Kuniyuki Iwashima , =?utf-8?q?Maciej_=C5=BBenczykowski?= , Menglong Dong , Akhmat Karakotov , Alexander Duyck Subject: [PATCH v1 1/3] net: Introduce sk_use_task_frag in struct sock. Date: Mon, 21 Nov 2022 08:35:17 -0500 Message-Id: In-Reply-To: References: MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.10 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org X-Patchwork-Delegate: kuba@kernel.org From: Guillaume Nault Sockets that can be used while recursing into memory reclaim, like those used by network block devices and file systems, mustn't use current->task_frag: if the current process is already using it, then the inner memory reclaim call would corrupt the task_frag structure. To avoid this, sk_page_frag() uses ->sk_allocation to detect sockets that mustn't use current->task_frag, assuming that those used during memory reclaim had their allocation constraints reflected in ->sk_allocation. This unfortunately doesn't cover all cases: in an attempt to remove all usage of GFP_NOFS and GFP_NOIO, sunrpc stopped setting these flags in ->sk_allocation, and used memalloc_nofs critical sections instead. This breaks the sk_page_frag() heuristic since the allocation constraints are now stored in current->flags, which sk_page_frag() can't read without risking triggering a cache miss and slowing down TCP's fast path. This patch creates a new field in struct sock, named sk_use_task_frag, which sockets with memory reclaim constraints can set to false if they can't safely use current->task_frag. In such cases, sk_page_frag() now always returns the socket's page_frag (->sk_frag). The first user is sunrpc, which needs to avoid using current->task_frag but can keep ->sk_allocation set to GFP_KERNEL otherwise. Eventually, it might be possible to simplify sk_page_frag() by only testing ->sk_use_task_frag and avoid relying on the ->sk_allocation heuristic entirely (assuming other sockets will set ->sk_use_task_frag according to their constraints in the future). The new ->sk_use_task_frag field is placed in a hole in struct sock and belongs to a cache line shared with ->sk_shutdown. Therefore it should be hot and shouldn't have negative performance impacts on TCP's fast path (sk_shutdown is tested just before the while() loop in tcp_sendmsg_locked()). Link: https://lore.kernel.org/netdev/b4d8cb09c913d3e34f853736f3f5628abfd7f4b6.1656699567.git.gnault@redhat.com/ Signed-off-by: Guillaume Nault --- include/net/sock.h | 11 +++++++++-- net/core/sock.c | 1 + 2 files changed, 10 insertions(+), 2 deletions(-) diff --git a/include/net/sock.h b/include/net/sock.h index d08cfe190a78..ffba9e95470d 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -318,6 +318,9 @@ struct sk_filter; * @sk_stamp: time stamp of last packet received * @sk_stamp_seq: lock for accessing sk_stamp on 32 bit architectures only * @sk_tsflags: SO_TIMESTAMPING flags + * @sk_use_task_frag: allow sk_page_frag() to use current->task_frag. + Sockets that can be used under memory reclaim should + set this to false. * @sk_bind_phc: SO_TIMESTAMPING bind PHC index of PTP virtual clock * for timestamping * @sk_tskey: counter to disambiguate concurrent tstamp requests @@ -504,6 +507,7 @@ struct sock { #endif u16 sk_tsflags; u8 sk_shutdown; + bool sk_use_task_frag; atomic_t sk_tskey; atomic_t sk_zckey; @@ -2536,14 +2540,17 @@ static inline void sk_stream_moderate_sndbuf(struct sock *sk) * socket operations and end up recursing into sk_page_frag() * while it's already in use: explicitly avoid task page_frag * usage if the caller is potentially doing any of them. - * This assumes that page fault handlers use the GFP_NOFS flags. + * This assumes that page fault handlers use the GFP_NOFS flags or + * explicitly disable sk_use_task_frag. * * Return: a per task page_frag if context allows that, * otherwise a per socket one. */ static inline struct page_frag *sk_page_frag(struct sock *sk) { - if ((sk->sk_allocation & (__GFP_DIRECT_RECLAIM | __GFP_MEMALLOC | __GFP_FS)) == + if (sk->sk_use_task_frag && + (sk->sk_allocation & (__GFP_DIRECT_RECLAIM | __GFP_MEMALLOC | + __GFP_FS)) == (__GFP_DIRECT_RECLAIM | __GFP_FS)) return ¤t->task_frag; diff --git a/net/core/sock.c b/net/core/sock.c index 788c1372663c..1ab781be9fbe 100644 --- a/net/core/sock.c +++ b/net/core/sock.c @@ -3314,6 +3314,7 @@ void sock_init_data(struct socket *sock, struct sock *sk) sk->sk_rcvbuf = READ_ONCE(sysctl_rmem_default); sk->sk_sndbuf = READ_ONCE(sysctl_wmem_default); sk->sk_state = TCP_CLOSE; + sk->sk_use_task_frag = true; sk_set_socket(sk, sock); sock_set_flag(sk, SOCK_ZAPPED);