Re: 2.6.1 sendfile regression

[Andrew Morton <akpm@osdl.org>]

Felix von Leitner <felix-kernel@fefe.de> wrote:
>
> I'm getting a huge sendfile regression in 2.6.1; when serving a large
> file on an IPv4 TCP socket via sendfile64, the transfer starts at about
> 4 MB (2.6.0: >7 MB) and the hard disk like stays on 100% (which normally
> only happens if the file is badly fragmented, fragmentation of this file
> is 0%).  Then, suddenly, the network performance drops dramatically,
> getting worse and worse.  strace shows that the process is hanging
> inside sendfile64 (which should not happen since the socket is
> non-blocking).  The process then stays inside sendfile for up to a
> minute or so and can't be interrupted or killed in that time.
> 

Probably it is the ill-advised readahead tweak.  Does the below patch fix
it up?

diff -puN mm/filemap.c~a mm/filemap.c
--- 25/mm/filemap.c~a	Fri Jan  9 16:20:32 2004
+++ 25-akpm/mm/filemap.c	Fri Jan  9 16:20:46 2004
@@ -596,12 +596,6 @@ void do_generic_mapping_read(struct addr
 	offset = *ppos & ~PAGE_CACHE_MASK;
 	last = (*ppos + desc->count) >> PAGE_CACHE_SHIFT;
 
-	/*
-	 * Let the readahead logic know upfront about all
-	 * the pages we'll need to satisfy this request
-	 */
-	for (; index < last; index++)
-		page_cache_readahead(mapping, ra, filp, index);
 	index = *ppos >> PAGE_CACHE_SHIFT;
 
 	for (;;) {

_