On Fri, Nov 01, 2013 at 01:07:45PM +0100, Peter Zijlstra wrote: > On Fri, Nov 01, 2013 at 07:44:29PM +0800, Yuanhan Liu wrote: > > commit 012f18004da33ba672e3c60838cc4898126174d3 > > Author: Rik van Riel <r...@redhat.com> > > Date: Mon Aug 9 17:18:40 2010 -0700 > > > > mm: always lock the root (oldest) anon_vma > > > > Always (and only) lock the root (oldest) anon_vma whenever we do > > something > > in an anon_vma. The recently introduced anon_vma scalability is due to > > the rmap code scanning only the VMAs that need to be scanned. Many > > common > > operations still took the anon_vma lock on the root anon_vma, so always > > taking that lock is not expected to introduce any scalability issues. > > > > However, always taking the same lock does mean we only need to take one > > lock, which means rmap_walk on pages from any anon_vma in the vma is > > excluded from occurring during an munmap, expand_stack or other > > operation > > that needs to exclude rmap_walk and similar functions. > > > > Also add the proper locking to vma_adjust. > > > > Signed-off-by: Rik van Riel <r...@redhat.com> > > Tested-by: Larry Woodman <lwood...@redhat.com> > > Acked-by: Larry Woodman <lwood...@redhat.com> > > Reviewed-by: Minchan Kim <minchan....@gmail.com> > > Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hir...@jp.fujitsu.com> > > Acked-by: Mel Gorman <m...@csn.ul.ie> > > Acked-by: Linus Torvalds <torva...@linux-foundation.org> > > Signed-off-by: Andrew Morton <a...@linux-foundation.org> > > Signed-off-by: Linus Torvalds <torva...@linux-foundation.org> > > Right that commit did.
Sorry again for that! I was jusy being brain dead :( > I'm still not sure why you change both the > locking proper and the locking primitive used in one patch set. convert rwsem to rwlock silightly depends on per anon_vma lock, as it's a bad idea to do avc allocation inside a spin lock. Without converting rwsem to rwlock, it's not that useful to introduce per anon_vma lock, or worse, it may introduce regressions. > > Also, changing the locking proper requires a very detailed explanation > on why it is correct; Thanks for the tip. And yes, this patch really lacks of some explanation. I tried to find some potentional races. I then digged the git history and found it was per anon_lock at the first time avc was introduced. It was changed to root locking not for fixing race, thus I think we can changed it back, and this time, for performance boost. anon_vma lock owns biggest lock contention on our many-core(say 120)servers from /proc/lock_stat. I found Ingo's patch makes it better, and since it's a spin lock, I then tried to narrow down the lock range. Hence, I wrote this patch. This patch may be wrong, but I guess it's somehow worthy sending out for comments. > we've had far too many 'fun' issues with the > anon_vma locking in the past. Yeah, I know. Say, http://lwn.net/Articles/383162/ ;) Thanks. --yliu -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
