Re: [PATCH 4/7] mm, vmscan: show LRU name in mm_vmscan_lru_isolate tracepoint

From: Michal Hocko
Date: Thu Dec 29 2016 - 02:57:37 EST

On Thu 29-12-16 15:02:04, Minchan Kim wrote:
> On Wed, Dec 28, 2016 at 04:30:29PM +0100, Michal Hocko wrote:
> > From: Michal Hocko <mhocko@xxxxxxxx>
> >
> > mm_vmscan_lru_isolate currently prints only whether the LRU we isolate
> > from is file or anonymous but we do not know which LRU this is. It is
> > useful to know whether the list is file or anonymous as well. Change
> > the tracepoint to show symbolic names of the lru rather.
> >
> > Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
> Not exactly same with this but idea is almost same.
> I used almost same tracepoint to investigate agging(i.e., deactivating) problem
> in 32b kernel with node-lru.
> It was enough. Namely, I didn't need tracepoint in shrink_active_list like your
> first patch.
> Your first patch is more straightforwad and information. But as you introduced
> this patch, I want to ask in here.
> Isn't it enough with this patch without your first one to find a such problem?

I assume this should be a reply to, right?
And you are right that for the particular problem it was enough to have
a tracepoint inside inactive_list_is_low and shrink_active_list one
wasn't really needed. On the other hand aging issues are really hard to
debug as well and so I think that both are useful. The first one tell us
_why_ we do aging while the later _how_ we do that.
Michal Hocko