linux-kernel - Re: [PATCH 06/14] perf tools: Cache dso data file descriptor

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Date:	Thu, 29 May 2014 11:01:25 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Jiri Olsa <jolsa@...nel.org>, linux-kernel@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Jean Pihet <jean.pihet@...aro.org>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 06/14] perf tools: Cache dso data file descriptor

On Thu, May 29, 2014 at 09:02:36AM +0900, Namhyung Kim wrote:
> On Tue, 27 May 2014 09:37:38 +0200, Jiri Olsa wrote:
> > On Tue, May 27, 2014 at 10:05:28AM +0900, Namhyung Kim wrote:
> >> Hi Jiri,
> >> 
> >> On Thu, 15 May 2014 19:23:27 +0200, Jiri Olsa wrote:
> >> 
> >> [SNIP]
> >> > +static void data_close(void)
> >> > +{
> >> > +	bool cache_fd = may_cache_fd();
> >> > +
> >> > +	if (!cache_fd)
> >> > +		close_first_dso();
> >> > +}
> >> 
> >> Why do you do this at close()?  As long as there's no attempt to open a
> >> new file, we can keep existing fd, no?
> >
> > so the way it works now is:
> >
> >  - we keep up to the 'RLIMIT_NOFILE / 2' of open dso objects
> >  - if we try to open dso and it fails, because we are out of
> >    file descriptors, we close dso objects and try to reopen
> >    (check do_open function)
> >  - when we close the dso object we check if number of opened
> >    dso objects is below 'RLIMIT_NOFILE / 2'.. if it is, we keep
> >    the dso opened, if not we close first dso in the list
> >
> > util/dso.h tries to describe that
> 
> Yes, I know.  But my question is why do this at close()?  Isn't it
> sufficient to check the file limit at open() and close previous one if
> necessary?

hm, it's still the same operation to be done either in open
or in close.. but we would not need dso__data_close then..
ok, I'll make the change ;-)

thanks,
jirka
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