SOLVED: Performance drop 2.6.0-test7 -> 2.6.1-rc2

[Jan Kasprzak <kas@informatics.muni.cz>]

Jan Kasprzak wrote:
: 	Yesterday I have upgraded the kernel on my FTP server to 2.6.1-rc2
: (from 2.6.0-test7) and today I have found the server struggling under
: load average of 40+ and the system was barely usable. The main load on the
: server is ProFTPd serving mainly ISO 9660 images using sendfile().

	For archives: Andrew Morton suggested to apply the following patch
to mm/filemap.c (which in fact reverts part of the patch-2.6.1), and this
solved the problem (bigger-than-needed read ahead when doing sendfile()
of large files). 2.6.1 with this patch works for me now. Thanks!

-Yenya

diff -puN mm/filemap.c~readahead-partial-backout mm/filemap.c
--- 25/mm/filemap.c~readahead-partial-backout	2004-01-09 22:19:32.000000000 -0800
+++ 25-akpm/mm/filemap.c	2004-01-09 22:19:32.000000000 -0800
@@ -587,22 +587,13 @@ void do_generic_mapping_read(struct addr
 			     read_actor_t actor)
 {
 	struct inode *inode = mapping->host;
-	unsigned long index, offset, last;
+	unsigned long index, offset;
 	struct page *cached_page;
 	int error;
 
 	cached_page = NULL;
 	index = *ppos >> PAGE_CACHE_SHIFT;
 	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 (;;) {
 		struct page *page;
@@ -621,6 +612,7 @@ void do_generic_mapping_read(struct addr
 		}
 
 		cond_resched();
+		page_cache_readahead(mapping, ra, filp, index);
 
 		nr = nr - offset;
 find_page:

_

-- 
| Jan "Yenya" Kasprzak  <kas at {fi.muni.cz - work | yenya.net - private}> |
| GPG: ID 1024/D3498839      Fingerprint 0D99A7FB206605D7 8B35FCDE05B18A5E |
| http://www.fi.muni.cz/~kas/   Czech Linux Homepage: http://www.linux.cz/ |
|  I actually have a lot of admiration and respect for the PATA knowledge  |
| embedded in drivers/ide. But I would never call it pretty:) -Jeff Garzik |