From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Hocko Subject: Re: [PATCH v2 2/3] mm: page_counter: rearrange struct page_counter fields Date: Thu, 25 Aug 2022 08:47:24 +0200 Message-ID: References: <20220825000506.239406-1-shakeelb@google.com> <20220825000506.239406-3-shakeelb@google.com> Mime-Version: 1.0 Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1661410045; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=zLRWmwcimgQLwECe4VlFsT+nEfyDLI69yDOnnoQ7NCo=; b=qL0xHbIA8DNVfkr/xEEsAFL6UM7wiK2Au3n1koR1lst2jLTaeQ5OPjq50FEyTFusso1VDB FirljZWBsdFYK23F4Hf/RYnI/zzzCntvRuUj0pxGiuZZ6GQxQ2f6MddIcLyqKENJRZesOl vsYJr4Vzc3Z5rMGNQ8svI56dp/Y4Aeg= Content-Disposition: inline In-Reply-To: <20220825000506.239406-3-shakeelb@google.com> List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Shakeel Butt Cc: Johannes Weiner , Roman Gushchin , Muchun Song , Michal =?iso-8859-1?Q?Koutn=FD?= , Eric Dumazet , Soheil Hassas Yeganeh , Feng Tang , Oliver Sang , Andrew Morton , lkp@lists.01.org, cgroups@vger.kernel.org, linux-mm@kvack.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org On Thu 25-08-22 00:05:05, Shakeel Butt wrote: > With memcg v2 enabled, memcg->memory.usage is a very hot member for > the workloads doing memcg charging on multiple CPUs concurrently. > Particularly the network intensive workloads. In addition, there is a > false cache sharing between memory.usage and memory.high on the charge > path. This patch moves the usage into a separate cacheline and move all > the read most fields into separate cacheline. > > To evaluate the impact of this optimization, on a 72 CPUs machine, we > ran the following workload in a three level of cgroup hierarchy. > > $ netserver -6 > # 36 instances of netperf with following params > $ netperf -6 -H ::1 -l 60 -t TCP_SENDFILE -- -m 10K > > Results (average throughput of netperf): > Without (6.0-rc1) 10482.7 Mbps > With patch 12413.7 Mbps (18.4% improvement) > > With the patch, the throughput improved by 18.4%. > > One side-effect of this patch is the increase in the size of struct > mem_cgroup. For example with this patch on 64 bit build, the size of > struct mem_cgroup increased from 4032 bytes to 4416 bytes. However for > the performance improvement, this additional size is worth it. In > addition there are opportunities to reduce the size of struct > mem_cgroup like deprecation of kmem and tcpmem page counters and > better packing. > > Signed-off-by: Shakeel Butt > Reported-by: kernel test robot > Reviewed-by: Feng Tang > Acked-by: Soheil Hassas Yeganeh > Acked-by: Roman Gushchin Acked-by: Michal Hocko One nit below > --- > Changes since v1: > - Updated the commit message > - Make struct page_counter cache align. > > include/linux/page_counter.h | 35 +++++++++++++++++++++++------------ > 1 file changed, 23 insertions(+), 12 deletions(-) > > diff --git a/include/linux/page_counter.h b/include/linux/page_counter.h > index 679591301994..78a1c934e416 100644 > --- a/include/linux/page_counter.h > +++ b/include/linux/page_counter.h > @@ -3,15 +3,26 @@ > #define _LINUX_PAGE_COUNTER_H > > #include > +#include > #include > #include > > +#if defined(CONFIG_SMP) > +struct pc_padding { > + char x[0]; > +} ____cacheline_internodealigned_in_smp; > +#define PC_PADDING(name) struct pc_padding name > +#else > +#define PC_PADDING(name) > +#endif > + > struct page_counter { > + /* > + * Make sure 'usage' does not share cacheline with any other field. The > + * memcg->memory.usage is a hot member of struct mem_cgroup. > + */ > atomic_long_t usage; > - unsigned long min; > - unsigned long low; > - unsigned long high; > - unsigned long max; > + PC_PADDING(_pad1_); > > /* effective memory.min and memory.min usage tracking */ > unsigned long emin; > @@ -23,18 +34,18 @@ struct page_counter { > atomic_long_t low_usage; > atomic_long_t children_low_usage; > > - /* legacy */ > unsigned long watermark; > unsigned long failcnt; These two are also touched in the charging path so we could squeeze them into the same cache line as usage. 0-day machinery was quite good at hitting noticeable regression anytime we have changed layout so let's see what they come up with after this patch ;) -- Michal Hocko SUSE Labs