From fb87bd47516d9a26b6d549231aa743b20fd4a569 Mon Sep 17 00:00:00 2001 From: Guillaume Nault Date: Fri, 16 Dec 2022 07:45:26 -0500 Subject: net: Introduce sk_use_task_frag in struct sock. 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 Reviewed-by: Benjamin Coddington Signed-off-by: Jakub Kicinski --- net/core/sock.c | 1 + 1 file changed, 1 insertion(+) (limited to 'net/core/sock.c') diff --git a/net/core/sock.c b/net/core/sock.c index d2587d8712db..f954d5893e79 100644 --- a/net/core/sock.c +++ b/net/core/sock.c @@ -3390,6 +3390,7 @@ 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); -- cgit v1.2.3