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Date: Tue, 6 May 2014 23:21:18 +0100 From: Mel Gorman <mgorman@...e.de> To: Peter Zijlstra <peterz@...radead.org> Cc: Linux-MM <linux-mm@...ck.org>, Linux-FSDevel <linux-fsdevel@...r.kernel.org>, Johannes Weiner <hannes@...xchg.org>, Vlastimil Babka <vbabka@...e.cz>, Jan Kara <jack@...e.cz>, Michal Hocko <mhocko@...e.cz>, Hugh Dickins <hughd@...gle.com>, Linux Kernel <linux-kernel@...r.kernel.org> Subject: Re: [PATCH 03/17] mm: page_alloc: Use jump labels to avoid checking number_of_cpusets On Tue, May 06, 2014 at 10:23:50PM +0200, Peter Zijlstra wrote: > On Thu, May 01, 2014 at 09:44:34AM +0100, Mel Gorman wrote: > > If cpusets are not in use then we still check a global variable on every > > page allocation. Use jump labels to avoid the overhead. > > > > Signed-off-by: Mel Gorman <mgorman@...e.de> > > --- > > include/linux/cpuset.h | 31 +++++++++++++++++++++++++++++++ > > kernel/cpuset.c | 8 ++++++-- > > mm/page_alloc.c | 3 ++- > > 3 files changed, 39 insertions(+), 3 deletions(-) > > > > diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h > > index b19d3dc..2b89e07 100644 > > --- a/include/linux/cpuset.h > > +++ b/include/linux/cpuset.h > > @@ -17,6 +17,35 @@ > > > > extern int number_of_cpusets; /* How many cpusets are defined in system? */ > > > > +#ifdef HAVE_JUMP_LABEL > > +extern struct static_key cpusets_enabled_key; > > +static inline bool cpusets_enabled(void) > > +{ > > + return static_key_false(&cpusets_enabled_key); > > +} > > +#else > > +static inline bool cpusets_enabled(void) > > +{ > > + return number_of_cpusets > 1; > > +} > > +#endif > > + > > +static inline void cpuset_inc(void) > > +{ > > + number_of_cpusets++; > > +#ifdef HAVE_JUMP_LABEL > > + static_key_slow_inc(&cpusets_enabled_key); > > +#endif > > +} > > + > > +static inline void cpuset_dec(void) > > +{ > > + number_of_cpusets--; > > +#ifdef HAVE_JUMP_LABEL > > + static_key_slow_dec(&cpusets_enabled_key); > > +#endif > > +} > > Why the HAVE_JUMP_LABEL and number_of_cpusets thing? When > !HAVE_JUMP_LABEL the static_key thing reverts to an atomic_t and > static_key_false() becomes: > Because number_of_cpusets is used to size a kmalloc(). Potentially I could abuse the internals of static keys and use the value of key->enabled but that felt like abuse of the API. -- Mel Gorman SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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