lkml.org 
[lkml]   [2012]   [Dec]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] mm: Downgrade mmap_sem before locking or populating on mmap
On Thu, Dec 13, 2012 at 09:49:43PM -0800, Andy Lutomirski wrote:
> This is a serious cause of mmap_sem contention. MAP_POPULATE
> and MCL_FUTURE, in particular, are disastrous in multithreaded programs.
>
> Signed-off-by: Andy Lutomirski <luto@amacapital.net>
> ---
>
> Sensible people use anonymous mappings. I write kernel patches :)
>
> I'm not entirely thrilled by the aesthetics of this patch. The MAP_POPULATE case
> could also be improved by doing it without any lock at all. This is still a big
> improvement, though.

Wait a minute. get_user_pages() relies on ->mmap_sem being held. Unless
I'm seriously misreading your patch it removes that protection. And yes,
I'm aware of execve-related exception; it's in special circumstances -
bprm->mm is guaranteed to be not shared (and we need to rearchitect that
area anyway, but that's a separate story).


\
 
 \ /
  Last update: 2012-12-14 09:01    [W:0.118 / U:0.756 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site