mmap() sendfile()

[Mike Silbersack]

On Mon, 12 Dec 2005, Cedric Tabary wrote:

> If it is true, doing a sendfile() on some very big files (even if not
> keeping the descriptor open after) will kill the cache ?
>
> Please help me to understand why this patch ? and the difference between
> sendfile() and mmap() at the memory or cache level..
>
> Cédric

My memory escapes me on all the details, but there were two potential 
reasons not to use sendfile with 4.x that no longer apply in 5.x and 
above:

1.  Sendfile used to send small files inefficiently, sending the http 
headers in one packet and the data in another.  I fixed this in 5.x.

2.  Alan Cox improved the memory efficiency of sendfile greatly, it now 
uses a single kernel buffer for all copies of the same block of the same 
file, whereas the old implementation made an in-kernel copy of each block, 
making it no more memory efficient than using mbufs.

So, if there was a reason to not use sendfile under 4.x, it's probably not 
true anymore.

Someone sent me a patch to thttpd which made it more efficient on FreeBSD 
a looooooong time ago, I don't recall what changes he had made.

Mike "Silby" Silbersack