| Message ID | 20230120181136.3764521-1-edumazet@google.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 057fb03160a88925877548979ab4ab7f9223e118 |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | [net-next] selftests: net: tcp_mmap: populate pages in send path | expand |
Hello: This patch was applied to netdev/net-next.git (master) by Jakub Kicinski <kuba@kernel.org>: On Fri, 20 Jan 2023 18:11:36 +0000 you wrote: > In commit 72653ae5303c ("selftests: net: tcp_mmap: > Use huge pages in send path") I made a change to use hugepages > for the buffer used by the client (tx path) > > Today, I understood that the cause for poor zerocopy > performance was that after a mmap() for a 512KB memory > zone, kernel uses a single zeropage, mapped 128 times. > > [...] Here is the summary with links: - [net-next] selftests: net: tcp_mmap: populate pages in send path https://git.kernel.org/netdev/net-next/c/057fb03160a8 You are awesome, thank you!
diff --git a/tools/testing/selftests/net/tcp_mmap.c b/tools/testing/selftests/net/tcp_mmap.c index 00f837c9bc6c4549c19dfc27aa2d08c454ea169e..46a02bbd31d0be4d54b2b372415bce6c0d538b22 100644 --- a/tools/testing/selftests/net/tcp_mmap.c +++ b/tools/testing/selftests/net/tcp_mmap.c @@ -137,7 +137,8 @@ static void *mmap_large_buffer(size_t need, size_t *allocated) if (buffer == (void *)-1) { sz = need; buffer = mmap(NULL, sz, PROT_READ | PROT_WRITE, - MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); + MAP_PRIVATE | MAP_ANONYMOUS | MAP_POPULATE, + -1, 0); if (buffer != (void *)-1) fprintf(stderr, "MAP_HUGETLB attempt failed, look at /sys/kernel/mm/hugepages for optimal performance\n"); }
In commit 72653ae5303c ("selftests: net: tcp_mmap: Use huge pages in send path") I made a change to use hugepages for the buffer used by the client (tx path) Today, I understood that the cause for poor zerocopy performance was that after a mmap() for a 512KB memory zone, kernel uses a single zeropage, mapped 128 times. This was really the reason for poor tx path performance in zero copy mode, because this zero page refcount is under high pressure, especially when TCP ACK packets are processed on another cpu. We need either to force a COW on all the memory range, or use MAP_POPULATE so that a zero page is not abused. Signed-off-by: Eric Dumazet <edumazet@google.com> --- tools/testing/selftests/net/tcp_mmap.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)