New sendfile(2) syscall. A joint effort of NGINX and Netflix from 2013 and

up to now.

The new sendfile is the code that Netflix uses to send their multiple tens
of gigabits of data per second. The new implementation features asynchronous
I/O, when I/O operations are launched, but not awaited to be complete. An
explanation of why such behavior is beneficial compared to old one is
going to be too long for a commit message, so we will skip it here.

Additional features of new syscall are extra flags, which provide an
application more control over data sent. The SF_NOCACHE flag tells
kernel that data shouldn't be cached after it was sent. The SF_READAHEAD()
macro allows to specify readahead size in pages.

The new syscalls is a drop in replacement. No modifications are required
to applications. One can take nginx binary for stable/10 and run it
successfully on head. Although SF_NODISKIO lost its original sense, as now
sendfile doesn't block, and now means something completely different (tm),
using the new sendfile the old way is absolutely safe.

Celebrates:	Netflix global launch!
Sponsored by:	Nginx, Inc.
Sponsored by:	Netflix
Relnotes:	yes

1 files changed, 3 insertions, 1 deletions

diff --git a/sys/sys/mbuf.h b/sys/sys/mbuf.h
index 8509a6c..91dd895 100644
--- a/sys/sys/mbuf.h
+++ b/sys/sys/mbuf.h
@@ -343,12 +343,13 @@ struct mbuf {
  * External mbuf storage buffer types.
  */
 #define	EXT_CLUSTER	1	/* mbuf cluster */
-#define	EXT_SFBUF	2	/* sendfile(2)'s sf_bufs */
+#define	EXT_SFBUF	2	/* sendfile(2)'s sf_buf */
 #define	EXT_JUMBOP	3	/* jumbo cluster page sized */
 #define	EXT_JUMBO9	4	/* jumbo cluster 9216 bytes */
 #define	EXT_JUMBO16	5	/* jumbo cluster 16184 bytes */
 #define	EXT_PACKET	6	/* mbuf+cluster from packet zone */
 #define	EXT_MBUF	7	/* external mbuf reference (M_IOVEC) */
+#define	EXT_SFBUF_NOCACHE 8	/* sendfile(2)'s sf_buf not to be cached */
 
 #define	EXT_VENDOR1	224	/* for vendor-internal use */
 #define	EXT_VENDOR2	225	/* for vendor-internal use */
@@ -397,6 +398,7 @@ struct mbuf {
  */
 void sf_ext_ref(void *, void *);
 void sf_ext_free(void *, void *);
+void sf_ext_free_nocache(void *, void *);
 
 /*
  * Flags indicating checksum, segmentation and other offload work to be