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Mon, 20 Jun 2022 01:16:24 -0700 (PDT) Date: Mon, 20 Jun 2022 16:16:20 +0800 From: Muchun Song To: David Hildenbrand Cc: akpm@linux-foundation.org, corbet@lwn.net, mike.kravetz@oracle.com, osalvador@suse.de, paulmck@kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, duanxiongchun@bytedance.com, smuchun@gmail.com Subject: Re: [PATCH v4 1/2] mm: memory_hotplug: enumerate all supported section flags Message-ID: References: <20220619133851.68184-1-songmuchun@bytedance.com> <20220619133851.68184-2-songmuchun@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1655712986; a=rsa-sha256; cv=none; b=MA7KynQoFWUPJ/3ssWPaAUP07NpVmVYMc21nxjewMWNqB036xwNicM0ElOD/N4ozNodXoy Rmq10UnZc7KD70Hp9c+oGZlPIU7RNqrHyzR5e6LqGj45diL9kndm+bKm+1S404oufPrQiJ CzSACYQOcWjEhF/9BrSVDxyAKX/iFM4= ARC-Authentication-Results: i=1; imf13.hostedemail.com; dkim=pass header.d=bytedance-com.20210112.gappssmtp.com header.s=20210112 header.b=DzyUJyKd; 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spf=pass (imf13.hostedemail.com: domain of songmuchun@bytedance.com designates 209.85.214.179 as permitted sender) smtp.mailfrom=songmuchun@bytedance.com X-Rspamd-Server: rspam06 X-Stat-Signature: yz6donebumfuq1dg514bp37a58dgytrw X-HE-Tag: 1655712985-910465 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 Mon, Jun 20, 2022 at 09:51:42AM +0200, David Hildenbrand wrote: > 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 :) > Oh, just my personal preference. I can replace those with defines in next version if you prefer it. :-) Thanks. > LGTM > > -- > Thanks, > > David / dhildenb > >