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| author | Eric Dumazet <edumazet@google.com> | 2020-08-20 20:11:16 +0300 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2020-08-21 02:14:53 +0300 |
| commit | 0d89419319ef68f8acc1b78377ad3e7523fead4a (patch) | |
| tree | f08c02e3cce3b6a2e536374fb12886651c72833d | |
| parent | 394fcd8a813456b3306c423ec4227ed874dfc08b (diff) | |
| download | linux-0d89419319ef68f8acc1b78377ad3e7523fead4a.tar.xz | |
selftests: net: tcp_mmap: use madvise(MADV_DONTNEED)
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>
Signed-off-by: David S. Miller <davem@davemloft.net>
| -rw-r--r-- | tools/testing/selftests/net/tcp_mmap.c | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/tools/testing/selftests/net/tcp_mmap.c b/tools/testing/selftests/net/tcp_mmap.c index a61b7b3da549..59ec0b59f7b7 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) { |