lkml.org 
[lkml]   [2006]   [Oct]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH 1/3] Fix COW D-cache aliasing on fork
From
From: Linus Torvalds <torvalds@osdl.org>
Date: Fri, 20 Oct 2006 15:02:39 -0700 (PDT)

> On Fri, 20 Oct 2006, Ralf Baechle wrote:
> > When I delete the call (not part of my patchset) it means 12% faster
> > fork. But I'm not proposing this for 2.6.19.
>
> I just suspect it means a _buggy_ fork.
>
> It so happens (I think), that fork is big enough that it probably flushes
> the L1 cache _anyway_.

My understanding is that this works because in Ralf's original patch
(which is the context in which he is removing the flush_cache_mm()
call), he uses kmap()/kunmap() to map the page(s) being accessed at a
kernel virtual address which will fall into the same cache color as
the user virtual address --> no alias problems.

Since he does this for every page touched on the kernel side during
dup_mmap(), the existing flush_cache_mm() call in dup_mmap() does in
fact become redundant.
-
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: 2006-10-21 00:25    [from the cache]
©2003-2011 Jasper Spaans