| Message ID | 20200820171118.1822853-2-edumazet@google.com |
|---|---|
| State | New |
| Headers | show |
| Series | [net-next,1/3] selftests: net: tcp_mmap: use madvise(MADV_DONTNEED) | expand |
diff --git a/tools/testing/selftests/net/tcp_mmap.c b/tools/testing/selftests/net/tcp_mmap.c index a61b7b3da5496285876b0e16b18a3060850b0803..59ec0b59f7b76ff75685bd96901d8237e0665b2b 100644 --- a/tools/testing/selftests/net/tcp_mmap.c +++ b/tools/testing/selftests/net/tcp_mmap.c @@ -179,6 +179,10 @@ void *child_thread(void *arg) total_mmap += zc.length; if (xflg) hash_zone(addr, zc.length); + /* It is more efficient to unmap the pages right now, + * instead of doing this in next TCP_ZEROCOPY_RECEIVE. + */ + madvise(addr, zc.length, MADV_DONTNEED); total += zc.length; } if (zc.recv_skip_hint) {
When TCP_ZEROCOPY_RECEIVE operation has been added, I made the mistake of automatically un-mapping prior content before mapping new pages. This has the unfortunate effect of adding potentially long MMU operations (like TLB flushes) while socket lock is held. Using madvise(MADV_DONTNEED) right after pages has been used has two benefits : 1) This releases pages sooner, allowing pages to be recycled if they were part of a page pool in a NIC driver. 2) No more long unmap operations while preventing immediate processing of incoming packets. The cost of the added system call is small enough. Arjun will submit a kernel patch allowing to opt out from the unmap attempt in tcp_zerocopy_receive() Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Arjun Roy <arjunroy@google.com> Cc: Soheil Hassas Yeganeh <soheil@google.com> --- tools/testing/selftests/net/tcp_mmap.c | 4 ++++ 1 file changed, 4 insertions(+)