On Wed, Sep 27, 2017 at 03:22:41PM +0200, Michal Hocko wrote: > On Wed 27-09-17 22:15:11, Minchan Kim wrote: > > On Wed, Sep 27, 2017 at 10:35:12AM +0200, Michal Hocko wrote: > > > On Wed 27-09-17 17:04:32, Minchan Kim wrote: > > > > On Wed, Sep 27, 2017 at 09:48:35AM +0200, Michal Hocko wrote: > > > > > On Wed 27-09-17 14:04:01, Minchan Kim wrote: > > > [...] > > > > > > The problem is users have disabled swap readahead by echo 0 > /proc/sys/ > > > > > > vm/page-cluster are regressed by this new interface /sys/kernel/mm/swap/ > > > > > > vma_ra_max_order. Because for disabling readahead completely, they should > > > > > > disable vma_ra_max_order as well as page-cluster from now on. > > > > > > > > > > > > So, goal of new config to notice new feature to admins so they can be aware > > > > > > of new konb vma_ra_max_order as well as page-cluster. > > > > > > I canont think other better idea to preventing such regression. > > > > > > > > > > > > http://lkml.kernel.org/r/%3C20170913014019.GB29422@bbox%3E > > > > > > > > > > So, how are you going to configure this when you do not know whether > > > > > zram will be used? In other words what should e.g. distribution set this > > > > > to? > > > > > > > > I have no idea. Unfortunately, it depends on them. If they want to use > > > > zram as swap, they should fix the script. Surely, I don't like it. > > > > Instead, I wanted that page-cluster zeroing disables both virtual/pysical > > > > swap readahead not to break current userspace. However, Huang doesn't > > > > liek it. > > > > If you have better idea, please suggest. > > > > > > I understand your frustration but config options are not there to bypass > > > proper design decisions. Why cannot we unconditionally disable all the > > > read ahead when zram is enabled? > > > > It's not a zram specific issue. Every users who have disabled swap readahead > > via page-cluster will be broken, too. > > Do you have any examples outside of zram? Also I do not see why we I'm not a god to know every usecases on earth. It's just knob and it's have been there for a long time with following semantic: Zero disables swap readahead completely. So, anyuser can use it by their reasons(e.g., small memory system) I don't want to play with pointless game "Hey, give me an example. If you couldn't, no worth to keep the semantic" on such long time simple/clear semantic. > simply cannot disable swap readahead when page-cluster is 0? That's was what I want really but Huang want to use two readahead algorithms in parallel so he wanted to keep two separated disable knobs. > -- > Michal Hocko > SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
