LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Johannes Weiner <hannes@cmpxchg.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: kamezawa.hiroyu@jp.fujitsu.com, nishimura@mxp.nes.nec.co.jp,
	balbir@linux.vnet.ibm.com, minchan.kim@gmail.com,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [patch 2/3] memcg: prevent endless loop when charging huge pages to near-limit group
Date: Tue, 1 Feb 2011 01:04:55 +0100	[thread overview]
Message-ID: <20110201000455.GB19534@cmpxchg.org> (raw)
In-Reply-To: <20110131144131.6733aa3a.akpm@linux-foundation.org>

On Mon, Jan 31, 2011 at 02:41:31PM -0800, Andrew Morton wrote:
> On Mon, 31 Jan 2011 15:03:54 +0100
> Johannes Weiner <hannes@cmpxchg.org> wrote:
> > @@ -1111,6 +1111,15 @@ static bool mem_cgroup_check_under_limit(struct mem_cgroup *mem)
> >  	return false;
> >  }
> >  
> > +static bool mem_cgroup_check_margin(struct mem_cgroup *mem, unsigned long bytes)
> > +{
> > +	if (!res_counter_check_margin(&mem->res, bytes))
> > +		return false;
> > +	if (do_swap_account && !res_counter_check_margin(&mem->memsw, bytes))
> > +		return false;
> > +	return true;
> > +}
> 
> argh.
> 
> If you ever have a function with the string "check" in its name, it's a
> good sign that you did something wrong.
> 
> Check what?  Against what?  Returning what?
> 
> mem_cgroup_check_under_limit() isn't toooo bad - the name tells you
> what's being checked and tells you what to expect the return value to
> mean.
> 
> But "res_counter_check_margin" and "mem_cgroup_check_margin" are just
> awful.  Something like
> 
> 	bool res_counter_may_charge(counter, bytes)
> 
> would be much clearer.

That makes sense for the hard limit.  But the oh-so-generic resource
counters also have a soft limit, and you don't ask for that when you
want to charge.  Right now, I do not feel creative enough to come up
with a symmetric-sounding counterpart.

> If we really want to stick with the "check" names (perhaps as an ironic
> reference to res_counter's past mistakes) then please at least document
> the sorry things?

I cowardly went with this option and have a patch below to fold into
this fix.

Maybe it would be better to use res_counter_margin(cnt) >= wanted
throughout the code.  Or still better, make memcg work on pages and
res_counters on unsigned longs so the locking is no longer needed,
together with an API for most obvious maths.  I will work something
out and submit it separately.

---
Subject: [patch fixup] res_counter: document res_counter_check_margin()

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---

diff --git a/include/linux/res_counter.h b/include/linux/res_counter.h
index 5cfd78a..a5930cb 100644
--- a/include/linux/res_counter.h
+++ b/include/linux/res_counter.h
@@ -182,6 +182,14 @@ static inline bool res_counter_check_under_limit(struct res_counter *cnt)
 	return ret;
 }
 
+/**
+ * res_counter_check_margin - check if the counter allows charging
+ * @cnt: the resource counter to check
+ * @bytes: the number of bytes to check the remaining space against
+ *
+ * Returns a boolean value on whether the counter can be charged
+ * @bytes or whether this would exceed the limit.
+ */
 static inline bool res_counter_check_margin(struct res_counter *cnt,
 					    unsigned long bytes)
 {

  parent reply	other threads:[~2011-02-01  0:05 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-01-31 14:03 Johannes Weiner
2011-01-31 14:03 ` [patch 1/3] memcg: prevent endless loop when charging huge pages Johannes Weiner
2011-01-31 22:27   ` Minchan Kim
2011-01-31 23:48   ` KAMEZAWA Hiroyuki
2011-01-31 14:03 ` [patch 2/3] memcg: prevent endless loop when charging huge pages to near-limit group Johannes Weiner
2011-01-31 22:41   ` Andrew Morton
2011-01-31 23:50     ` KAMEZAWA Hiroyuki
2011-02-01  0:04     ` Johannes Weiner [this message]
2011-02-01  0:24       ` Andrew Morton
2011-02-01  0:34         ` Johannes Weiner
2011-02-03 12:53         ` [patch 0/2] memcg: clean up limit checking Johannes Weiner
2011-02-03 12:54           ` [patch 1/2] memcg: soft limit reclaim should end at limit not below Johannes Weiner
2011-02-03 23:41             ` KAMEZAWA Hiroyuki
2011-02-04  4:10             ` Balbir Singh
2011-02-03 12:56           ` [patch 2/2] memcg: simplify the way memory limits are checked Johannes Weiner
2011-02-03 23:44             ` KAMEZAWA Hiroyuki
2011-02-04  4:12             ` Balbir Singh
2011-01-31 22:42   ` [patch 2/3] memcg: prevent endless loop when charging huge pages to near-limit group Minchan Kim
2011-01-31 14:03 ` [patch 3/3] memcg: never OOM when charging huge pages Johannes Weiner
2011-01-31 22:52   ` Minchan Kim
2011-01-31 23:51   ` KAMEZAWA Hiroyuki

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20110201000455.GB19534@cmpxchg.org \
    --to=hannes@cmpxchg.org \
    --cc=akpm@linux-foundation.org \
    --cc=balbir@linux.vnet.ibm.com \
    --cc=kamezawa.hiroyu@jp.fujitsu.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=minchan.kim@gmail.com \
    --cc=nishimura@mxp.nes.nec.co.jp \
    --subject='Re: [patch 2/3] memcg: prevent endless loop when charging huge pages to near-limit group' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).