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 EF1D4ECAAD8 for ; Fri, 23 Sep 2022 06:31:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230475AbiIWGbJ (ORCPT ); Fri, 23 Sep 2022 02:31:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47784 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230428AbiIWGah (ORCPT ); Fri, 23 Sep 2022 02:30:37 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C2426EBD68 for ; Thu, 22 Sep 2022 23:30:15 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 2E0C9612F0 for ; Fri, 23 Sep 2022 06:30:15 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 28273C433C1; Fri, 23 Sep 2022 06:30:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1663914614; bh=6wH6fvRDvKDVnkaY/nhgbbeptQD/JxcR37eZDSHXOGg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=q7GFUCDcONGqNCXyzmvjczCXMoafWH750VuOJjdEoI2LSqW9lAHcuCbgDXvXmZKTa ESkdsAPTl3O73W4FK9kgQvxN3FxAxv0wdWbABSBPNIYhL4YU6lqLc7JppR0zksZB+a kKHFWLyMN1FkZvI/nQ9BcfxT7AcrfmvMBUKjRtvw= Date: Fri, 23 Sep 2022 08:30:45 +0200 From: Greg Kroah-Hartman To: Yury Norov Cc: Andy Shevchenko , linux-kernel@vger.kernel.org, Rasmus Villemoes , Phil Auld , Petr =?utf-8?Q?=C5=A0tetiar?= 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=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 22, 2022 at 01:41:40PM -0700, Yury Norov wrote: > + Petr Štetiar , > + Greg Kroah-Hartman > > 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. > > 1861 > > > > > 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) > > The defs below will be nicer if you make it like this: > > #define __CPULIST_FOR_10(x) (((x + 1) / 2 - 0) * 2) > #define __CPULIST_FOR_100(x) __CPULIST_FOR_10(10) + (((x + 1) / 2 - 5) * 3) > #define __CPULIST_FOR_1000(x) __CPULIST_FOR_100(100) + (((x + 1) / 2 - 50) * 4) > ... > > > > > +#if NR_CPUS < 1861 > > +#define CPULIST_FILE_MAX_BYTES PAGE_SIZE > > The comment says: > for more than 1170 and less than 1861 CPUs the page size is preserved. > > Which doesn't look correct. Looks like it should be: > for less than 1861 CPUs the page size is preserved. > > Or I miss something? > > > +#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 > > I'm OK to take this in replace for Phil's version, but the commit that > introduces CPULIST_FILE_MAX_BYTES is already in mainline: 7ee951acd31a8 > ("drivers/base: fix userspace break from using bin_attributes for cpumap > and cpulist"). Can you rebase it on top of v6.0-rc6? > > Greg, since Andy's version is more precise, I'd like to send a pull > request with it in -rc7. Can you drop Phil's patch so I'll go with > this one? Let me get this fix to Linus now for 6.0-final as it is hitting people right now. Making it "cleaner" after that is fine to go through your tree as that's less of an issue, right? thanks, greg k-h