linux-kernel - Re: [PATCH 07/15] mm: Add ___GFP

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Message-ID: <1425333845.20819.60.camel@picadillo>
Date:	Mon, 02 Mar 2015 16:04:05 -0600
From:	Tom Zanussi <tom.zanussi@...ux.intel.com>
To:	Alexei Starovoitov <ast@...mgrid.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Andi Kleen <andi@...stfloor.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 07/15] mm: Add ___GFP_NOTRACE

On Mon, 2015-03-02 at 11:29 -0800, Alexei Starovoitov wrote:
> On Mon, Mar 2, 2015 at 10:54 AM, Tom Zanussi
> <tom.zanussi@...ux.intel.com> wrote:
> >> >
> >> > The idea would be that instead of getting your individually kmalloc'ed
> >> > elements on-demand from kmalloc while in the handler, you'd get them
> >> > from a pool you've pre-allocated when you set up the table.  This could
> >> > be from a list of individual entries you've already kmalloc'ed ahead of
> >> > time, or from an array of n * sizeof(entry).
> >>
> >> would work, but kinda ugly, since we will pre-allocate a lot
> >> and may not be using it at all.
> >>
> >
> > That's true but you have a user-defined map limit anyway, which you can
> > adjust to minimize wastage.  And allocating ahead of time also means you
> > perturb the system less while actually tracing.
> 
> nope. it's the other way around.
> using kmalloc is faster and less overhead on the whole system
> then grabbing cache-cold objects from special pool.

Until you start causing GFP_ATOMIC failures for what you're tracing
because your map has grabbed them all...

Tom

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