On Thu, 7 Oct 2010 09:26:08 +0530 Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx> wrote: > * KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> [2010-10-07 12:18:16]: > > > On Thu, 7 Oct 2010 08:42:04 +0530 > > Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx> wrote: > > > > > * KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> [2010-10-07 08:58:58]: > > > > > > > On Wed, 6 Oct 2010 19:53:14 +0530 > > > > Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx> wrote: > > > > > > > > > I propose restricting page_cgroup.flags to 16 bits. The patch for the > > > > > same is below. Comments? > > > > > > > > > > > > > > > Restrict the bits usage in page_cgroup.flags > > > > > > > > > > From: Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx> > > > > > > > > > > Restricting the flags helps control growth of the flags unbound. > > > > > Restriciting it to 16 bits gives us the possibility of merging > > > > > cgroup id with flags (atomicity permitting) and saving a whole > > > > > long word in page_cgroup > > > > > > > > > > Signed-off-by: Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx> > > > > > > > > Doesn't make sense until you show the usage of existing bits. > > > > > > ?? > > > > > Limiting something for NOT EXISTING PATCH doesn't make sense, in general. > > > > > > > > And I guess 16bit may be too large on 32bit systems. > > > > > > too large on 32 bit systems? My intention is to keep the flags to 16 > > > bits and then use cgroup id for the rest and see if we can remove > > > mem_cgroup pointer > > > > > > > You can't use flags field to store mem_cgroup_id while we use lock bit on it. > > We have to store something more stable...as pfn or node-id or zone-id. > > > > It's very racy. > > > > Yes, correct it is racy, there is no easy way from what I know we can write > the upper 16 bits of the flag without affecting the lower 16 bits, if > the 16 bits are changing. One of the techniques could be to have lock > for the unsigned long word itself - but I don't know what performance > overhead that would add. Having said that I would like to explore > techniques that allow me to merge the two. > to store pfn, we need to limit under 12bit. I'll schedule my patch if dirty_ratio one goes. Thanks, -Kame -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>