Messages in this thread | | | Date | Mon, 17 Aug 2015 12:58:17 +0100 | From | Mel Gorman <> | Subject | Re: [PATCH 04/10] mm, page_alloc: Remove unnecessary taking of a seqlock when cpusets are disabled |
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On Wed, Aug 12, 2015 at 05:16:50PM -0700, David Rientjes wrote: > On Wed, 12 Aug 2015, Mel Gorman wrote: > > > There is a seqcounter that protects against spurious allocation failures > > when a task is changing the allowed nodes in a cpuset. There is no need > > to check the seqcounter until a cpuset exists. > > > > Signed-off-by: Mel Gorman <mgorman@techsingularity.net> > > Acked-by: David Rientjes <rientjes@google.com> > > Acked-by: Vlastimil Babka <vbabka@suse.cz> > > --- > > include/linux/cpuset.h | 6 ++++++ > > 1 file changed, 6 insertions(+) > > > > diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h > > index 1b357997cac5..6eb27cb480b7 100644 > > --- a/include/linux/cpuset.h > > +++ b/include/linux/cpuset.h > > @@ -104,6 +104,9 @@ extern void cpuset_print_task_mems_allowed(struct task_struct *p); > > */ > > static inline unsigned int read_mems_allowed_begin(void) > > { > > + if (!cpusets_enabled()) > > + return 0; > > + > > return read_seqcount_begin(¤t->mems_allowed_seq); > > } > > > > @@ -115,6 +118,9 @@ static inline unsigned int read_mems_allowed_begin(void) > > */ > > static inline bool read_mems_allowed_retry(unsigned int seq) > > { > > + if (!cpusets_enabled()) > > + return false; > > + > > return read_seqcount_retry(¤t->mems_allowed_seq, seq); > > } > > > > This patch is an obvious improvement, but I think it's also possible to > change this to be > > if (nr_cpusets() <= 1) > return false; > > and likewise in the existing cpusets_enabled() check in > get_page_from_freelist(). A root cpuset may not exclude mems on the > system so, even if mounted, there's no need to check or be worried about > concurrent change when there is only one cpuset.
Good idea. I'll make this a separate patch on top and rename cpuset_enabled to cpuset_mems_enabled to be clear about what it's checking.
Thanks.
-- Mel Gorman SUSE Labs
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