lkml.org 
[lkml]   [2014]   [Jul]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [patch] mm: memcontrol: use page lists for uncharge batching
On Fri 18-07-14 11:07:19, Johannes Weiner wrote:
> On Thu, Jul 17, 2014 at 05:29:36PM +0200, Michal Hocko wrote:
> > On Mon 07-07-14 14:55:58, Johannes Weiner wrote:
> > > Pages are now uncharged at release time, and all sources of batched
> > > uncharges operate on lists of pages. Directly use those lists, and
> > > get rid of the per-task batching state.
> > >
> > > This also batches statistics accounting, in addition to the res
> > > counter charges, to reduce IRQ-disabling and re-enabling.
> >
> > It is probably worth noticing that there is a higher chance of missing
> > threshold events now when we can accumulate huge number of uncharges
> > during munmaps. I do not think this is earth shattering and the overall
> > improvement is worth it but changelog should mention it.
>
> Does this actually matter, though? We might deliver events a few
> pages later than before, but as I read the threshold code, once
> invoked it catches up from the last delivered threshold to the new
> usage. So we shouldn't *miss* any events.

You are right. I have completely miss this aspect of threshold
implementation. I should have looked into the code before claiming that
:/ and not focus only on the triggering code. Sorry about that!

> > > Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
> >
> > With the follow up fix from
> > http://marc.info/?l=linux-mm&m=140552814228135&w=2
> >
> > Acked-by: Michal Hocko <mhocko@suse.cz>
>
> Thanks!
>
> > > +static void uncharge_list(struct list_head *page_list)
> > > +{
> > > + struct mem_cgroup *memcg = NULL;
> > > + unsigned long nr_memsw = 0;
> > > + unsigned long nr_anon = 0;
> > > + unsigned long nr_file = 0;
> > > + unsigned long nr_huge = 0;
> > > + unsigned long pgpgout = 0;
> > > + unsigned long nr_mem = 0;
> > > + struct list_head *next;
> > > + struct page *page;
> > > +
> > > + next = page_list->next;
> > > + do {
> >
> > I would use list_for_each_entry here which would also save list_empty
> > check in mem_cgroup_uncharge_list
>
> list_for_each_entry() wouldn't work for the singleton list where we
> pass in page->lru. That's why it's a do-while that always does the
> first page before checking whether it looped back to the list head.
>
> Do we need a comment for that? I'm not convinced, there are only two
> callsites, and the one that passes the singleton page->lru is right
> below this function.

--
Michal Hocko
SUSE Labs


\
 
 \ /
  Last update: 2014-07-21 15:21    [W:0.430 / U:0.832 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site