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[2003:d8:2f04:2500:cdb0:9b78:d423:43f]) by smtp.gmail.com with ESMTPSA id v6-20020adfa1c6000000b0021b8905e797sm5510805wrv.69.2022.06.20.00.51.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 20 Jun 2022 00:51:43 -0700 (PDT) Message-ID: Date: Mon, 20 Jun 2022 09:51:42 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.0 Subject: Re: [PATCH v4 1/2] mm: memory_hotplug: enumerate all supported section flags To: Muchun Song , akpm@linux-foundation.org, corbet@lwn.net, mike.kravetz@oracle.com, osalvador@suse.de, paulmck@kernel.org Cc: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, duanxiongchun@bytedance.com, smuchun@gmail.com References: <20220619133851.68184-1-songmuchun@bytedance.com> <20220619133851.68184-2-songmuchun@bytedance.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20220619133851.68184-2-songmuchun@bytedance.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1655711513; a=rsa-sha256; cv=none; b=SQotsynoe/fBVSpx9ydNAQCRYItjop9gcOq/YwzPoO7d0G91HIlSmDvPVHzRRKWpTU3x+G C/GUufd/KupcxbZIavQpimAF5MP71NwFRdcer52iZihJBuqHFsB6h4vmjVetozzrmUg77f wyrYpdNOzU7YupoJkz4l05QXpQmDrGw= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1655711513; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=yjoa1DMFRC4sDiSMpzTkndxHuKmwJoDSdtI3MTSI+I4=; b=4ui8Lp8JGscjhll3ndKWvIwcC/nBTM8MeJaXDrrRuu+OzJsaQBC/jPYBjtM0z2P3c7VnzJ kKzZ0GoiqLsH8ViHE7TkrB3QOtGw6IEFJrN6BsEFRuGmZEpxStFFdo+BtnNFgwns2OdPVl eKlVJquMAQC42ysJIZ7Ah4Zl+XqnFNI= ARC-Authentication-Results: i=1; imf28.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=fpn1nCON; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf28.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 170.10.129.124) smtp.mailfrom=david@redhat.com Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=fpn1nCON; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf28.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 170.10.129.124) smtp.mailfrom=david@redhat.com X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: B1FB5C000E X-Stat-Signature: i1eqkppmwt9p4hrgou6er94wn35pcouf X-HE-Tag: 1655711512-391981 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 19.06.22 15:38, Muchun Song wrote: > We are almost running out of section flags, only one bit is available in > the worst case (powerpc with 256k pages). However, there are still some > free bits (in ->section_mem_map) on other architectures (e.g. x86_64 has > 10 bits available, arm64 has 8 bits available with worst case of 64K > pages). We have hard coded those numbers in code, it is inconvenient to > use those bits on other architectures except powerpc. So transfer those > section flags to enumeration to make it easy to add new section flags in > the future. Also, move SECTION_TAINT_ZONE_DEVICE into the scope of > CONFIG_ZONE_DEVICE to save a bit on non-zone-device case. > > Signed-off-by: Muchun Song > --- > include/linux/mmzone.h | 44 +++++++++++++++++++++++++++++++++++--------- > mm/memory_hotplug.c | 6 ++++++ > mm/sparse.c | 2 +- > 3 files changed, 42 insertions(+), 10 deletions(-) > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index aab70355d64f..932843c6459b 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -1418,16 +1418,35 @@ extern size_t mem_section_usage_size(void); > * (equal SECTION_SIZE_BITS - PAGE_SHIFT), and the > * worst combination is powerpc with 256k pages, > * which results in PFN_SECTION_SHIFT equal 6. > - * To sum it up, at least 6 bits are available. > + * To sum it up, at least 6 bits are available on all architectures. > + * However, we can exceed 6 bits on some other architectures except > + * powerpc (e.g. 15 bits are available on x86_64, 13 bits are available > + * with the worst case of 64K pages on arm64) if we make sure the > + * exceeded bit is not applicable to powerpc. > */ > -#define SECTION_MARKED_PRESENT (1UL<<0) > -#define SECTION_HAS_MEM_MAP (1UL<<1) > -#define SECTION_IS_ONLINE (1UL<<2) > -#define SECTION_IS_EARLY (1UL<<3) > -#define SECTION_TAINT_ZONE_DEVICE (1UL<<4) > -#define SECTION_MAP_LAST_BIT (1UL<<5) > -#define SECTION_MAP_MASK (~(SECTION_MAP_LAST_BIT-1)) > -#define SECTION_NID_SHIFT 6 > +enum { > + SECTION_MARKED_PRESENT_BIT, > + SECTION_HAS_MEM_MAP_BIT, > + SECTION_IS_ONLINE_BIT, > + SECTION_IS_EARLY_BIT, > +#ifdef CONFIG_ZONE_DEVICE > + SECTION_TAINT_ZONE_DEVICE_BIT, > +#endif > + SECTION_MAP_LAST_BIT, > +}; > + > +enum { > + SECTION_MARKED_PRESENT = BIT(SECTION_MARKED_PRESENT_BIT), > + SECTION_HAS_MEM_MAP = BIT(SECTION_HAS_MEM_MAP_BIT), > + SECTION_IS_ONLINE = BIT(SECTION_IS_ONLINE_BIT), > + SECTION_IS_EARLY = BIT(SECTION_IS_EARLY_BIT), > +#ifdef CONFIG_ZONE_DEVICE > + SECTION_TAINT_ZONE_DEVICE = BIT(SECTION_TAINT_ZONE_DEVICE_BIT), > +#endif > +}; I can understand the reason for the other enum, to auto-assing numbers. What's the underlying reason for the enum here? Personally, I'd just stay with defines, so I'm curious :) LGTM -- Thanks, David / dhildenb