From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id AD56DC54EE9 for ; Fri, 23 Sep 2022 00:38:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231192AbiIWAiR (ORCPT ); Thu, 22 Sep 2022 20:38:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44220 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229771AbiIWAiO (ORCPT ); Thu, 22 Sep 2022 20:38:14 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DAE1D106A07 for ; Thu, 22 Sep 2022 17:38:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1663893493; h=from:from:reply-to:subject:subject: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=Zk1+EgBiZaGHGemzxW1+05s07p+KTnrxlBzg9GZkgF4=; b=RL3gRldBFbP/CGZeyF6+Gr6fxnHUaqnHAM8NbwVbD5rINNVHVXnFMhetdA1V8rDL4IkSEr 7zPWwlIsgZbGD05J0Q+p4C1AvKqybuTUd1pMxUbbJ6EeoBulaMVBvktoLNX/19LKbbmNcj UAvQS75odQ44VXaHqIstc9Qi0BMZvRA= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-258-Hbh2bazNPWqKme8RzUCvqA-1; Thu, 22 Sep 2022 20:38:08 -0400 X-MC-Unique: Hbh2bazNPWqKme8RzUCvqA-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 8651C85A5A6; Fri, 23 Sep 2022 00:38:08 +0000 (UTC) Received: from lorien.usersys.redhat.com (unknown [10.22.33.123]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 4727240C6EC2; Fri, 23 Sep 2022 00:38:08 +0000 (UTC) Date: Thu, 22 Sep 2022 20:38:06 -0400 From: Phil Auld To: Andy Shevchenko Cc: Yury Norov , linux-kernel@vger.kernel.org, Rasmus Villemoes Subject: Re: [PATCH v2 1/1] cpumask: Don't waste memory for sysfs cpulist nodes Message-ID: References: <20220922194954.1078-1-andriy.shevchenko@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220922194954.1078-1-andriy.shevchenko@linux.intel.com> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Andy, On Thu, Sep 22, 2022 at 10:49:54PM +0300 Andy Shevchenko wrote: > Currently the approximation is used which wastes the more memory > the more CPUs are present on the system. Proposed change calculates > the exact maximum needed in the worst case: > > NR_CPUS old new > ------- --- --- > 1 .. 1170 4096 4096 > 1171 .. 1860 4098 .. 6510 4096 > ... ... ... > 2*4096 28672 19925 > 4*4096 57344 43597 > 8*4096 114688 92749 > 16*4096 229376 191053 > 32*4096 458752 403197 > 64*4096 917504 861949 > 128*4096 1835008 1779453 > 256*4096 3670016 3670016 > > Under the hood the reccurent formula is being used: > (5 - 0) * 2 + > (50 - 5) * 3 + > (500 - 50) * 4 + > (5000 - 500) * 5 + > ... > (X[i] - X[i-1]) * i > > which allows to count the exact maximum length in the worst case, > i.e. when each second CPU is being listed. For backward compatibility > for more than 1170 and less than 1861 CPUs the page size is preserved. > > For less than 1171 and more than 1 million CPUs the old is being used. The memory is not really wasted since it's probably temporary in userspace and in the kernel it _is_ temporary and is only the length of the kasprintf string, which is most of the time much less. But that said, it is more accurate than the previous estimate. I was wondering if you were going to try to come up with a suitable compile time macro :) I tested 2, 8192 and 16k since the kernel does not want to build for other reasons with NR_CPUS at 32k. Reviewed-by: Phil Auld Tested-by: Phil Auld > > Signed-off-by: Andy Shevchenko > --- > v2: described better the advantage for 1171..1860 CPUs cases > include/linux/cpumask.h | 48 +++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 48 insertions(+) > > diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h > index 1b442fb2001f..12cf0905ca74 100644 > --- a/include/linux/cpumask.h > +++ b/include/linux/cpumask.h > @@ -1122,6 +1122,21 @@ cpumap_print_list_to_buf(char *buf, const struct cpumask *mask, > * > * for cpumap NR_CPUS * 9/32 - 1 should be an exact length. > * > + * for cpulist the reccurent formula is being used: > + * (5 - 0) * 2 + > + * (50 - 5) * 3 + > + * (500 - 50) * 4 + > + * (5000 - 500) * 5 + > + * ... > + * (X[i] - X[i-1]) * i > + * > + * which allows to count the exact maximum length in the worst case, > + * i.e. when each second CPU is being listed. For backward compatibility > + * for more than 1170 and less than 1861 CPUs the page size is preserved. > + * > + * For less than 1171 and more than 1 million CPUs the old is being used > + * as described below: > + * > * For cpulist 7 is (ceil(log10(NR_CPUS)) + 1) allowing for NR_CPUS to be up > * to 2 orders of magnitude larger than 8192. And then we divide by 2 to > * cover a worst-case of every other cpu being on one of two nodes for a > @@ -1132,6 +1147,39 @@ cpumap_print_list_to_buf(char *buf, const struct cpumask *mask, > */ > #define CPUMAP_FILE_MAX_BYTES (((NR_CPUS * 9)/32 > PAGE_SIZE) \ > ? (NR_CPUS * 9)/32 - 1 : PAGE_SIZE) > + > +#define __CPULIST_FOR_10(x) (((x + 1) / 2 - 0) * 2) > +#define __CPULIST_FOR_100(x) (((x + 1) / 2 - 5) * 3) > +#define __CPULIST_FOR_1000(x) (((x + 1) / 2 - 50) * 4) > +#define __CPULIST_FOR_10000(x) (((x + 1) / 2 - 500) * 5) > +#define __CPULIST_FOR_100000(x) (((x + 1) / 2 - 5000) * 6) > +#define __CPULIST_FOR_1000000(x) (((x + 1) / 2 - 50000) * 7) > + > +#if NR_CPUS < 1861 > +#define CPULIST_FILE_MAX_BYTES PAGE_SIZE > +#elif NR_CPUS < 10000 > +#define CPULIST_FILE_MAX_BYTES \ > + (__CPULIST_FOR_10(10) + \ > + __CPULIST_FOR_100(100) + \ > + __CPULIST_FOR_1000(1000) + \ > + __CPULIST_FOR_10000(NR_CPUS)) > +#elif NR_CPUS < 100000 > +#define CPULIST_FILE_MAX_BYTES \ > + (__CPULIST_FOR_10(10) + \ > + __CPULIST_FOR_100(100) + \ > + __CPULIST_FOR_1000(1000) + \ > + __CPULIST_FOR_10000(10000) + \ > + __CPULIST_FOR_100000(NR_CPUS)) > +#elif NR_CPUS < 1000000 > +#define CPULIST_FILE_MAX_BYTES \ > + (__CPULIST_FOR_10(10) + \ > + __CPULIST_FOR_100(100) + \ > + __CPULIST_FOR_1000(1000) + \ > + __CPULIST_FOR_10000(10000) + \ > + __CPULIST_FOR_100000(100000) + \ > + __CPULIST_FOR_1000000(NR_CPUS)) > +#else > #define CPULIST_FILE_MAX_BYTES (((NR_CPUS * 7)/2 > PAGE_SIZE) ? (NR_CPUS * 7)/2 : PAGE_SIZE) > +#endif > > #endif /* __LINUX_CPUMASK_H */ > -- > 2.35.1 > Cheers, Phil --