lkml.org 
[lkml]   [2002]   [Oct]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [patch] mmap-speedup-2.5.42-C3

On 15 Oct 2002, Andi Kleen wrote:

> When you oprofile KDE startup you notice that a lot of time is spent in
> get_unmapped_area too. The reason is that every KDE process links with
> 10-20 libraries and ends up with a 40-50 entry /proc/<pid>/maps.

actually, library mappings alone should not cause a slowdown, since we
start the search at MAP_UNMAPPED_BASE and most library mappings are below
1GB. But if those libraries use mmap()-ed anonymous RAM that has different
protections then the anonymous areas do not get merged and the scanning
overhead goes up.

> Optimizing this case would be likely useful too, although I suspect
> Ingo's last hit cache would already help somewhat.

well, could you check how much of an impact it has on KDE's kernel
profile? For the threaded test it's was a more than 10x application
speedup, and in the kernel profile get_unmapped_area() was like 90% of the
hits - after the change it was like 1% of the hits. (but, this test is the
best-case for the search cache, so ...)

if this simpler approach solves two different problem categories
sufficiently then i cannot see any reason to go for the much more complex
(and still not 100% scanning-less) approach.

Ingo


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:30    [W:0.044 / U:0.260 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site