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[195.135.220.15]) by mx.google.com with ESMTPS id 7si141717ejx.310.2019.06.11.03.37.30 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 11 Jun 2019 03:37:30 -0700 (PDT) Received-SPF: pass (google.com: domain of jack@suse.cz designates 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=pass (google.com: domain of jack@suse.cz designates 195.135.220.15 as permitted sender) smtp.mailfrom=jack@suse.cz X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id BB1C8AD12; Tue, 11 Jun 2019 10:37:29 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 1C7AE1E3E26; Tue, 11 Jun 2019 12:37:29 +0200 (CEST) Date: Tue, 11 Jun 2019 12:37:29 +0200 From: Jan Kara To: "Aneesh Kumar K.V" Cc: dan.j.williams@intel.com, linux-nvdimm@lists.01.org, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH v3 3/6] mm/nvdimm: Add page size and struct page size to pfn superblock Message-ID: <20190611103729.GA27635@quack2.suse.cz> References: <20190604091357.32213-1-aneesh.kumar@linux.ibm.com> <20190604091357.32213-3-aneesh.kumar@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190604091357.32213-3-aneesh.kumar@linux.ibm.com> User-Agent: Mutt/1.10.1 (2018-07-13) 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 Tue 04-06-19 14:43:54, Aneesh Kumar K.V wrote: > This is needed so that we don't wrongly initialize a namespace > which doesn't have enough space reserved for holding struct pages > with the current kernel. > > We also increment PFN_MIN_VERSION to make sure that older kernel > won't initialize namespace created with newer kernel. > > Signed-off-by: Aneesh Kumar K.V ... > diff --git a/drivers/nvdimm/pfn_devs.c b/drivers/nvdimm/pfn_devs.c > index 00c57805cad3..e01eee9efafe 100644 > --- a/drivers/nvdimm/pfn_devs.c > +++ b/drivers/nvdimm/pfn_devs.c > @@ -467,6 +467,15 @@ int nd_pfn_validate(struct nd_pfn *nd_pfn, const char *sig) > if (__le16_to_cpu(pfn_sb->version_minor) < 2) > pfn_sb->align = 0; > > + if (__le16_to_cpu(pfn_sb->version_minor) < 3) { > + /* > + * For a large part we use PAGE_SIZE. But we > + * do have some accounting code using SZ_4K. > + */ > + pfn_sb->page_struct_size = cpu_to_le16(64); > + pfn_sb->page_size = cpu_to_le32(SZ_4K); > + } > + > switch (le32_to_cpu(pfn_sb->mode)) { > case PFN_MODE_RAM: > case PFN_MODE_PMEM: As we discussed with Aneesh privately, this actually means that existing NVDIMM namespaces on PPC64 will stop working due to these defaults for old superblocks. I don't think that's a good thing as upgrading kernels is going to be nightmare due to this on PPC64. So I believe we should make defaults for old superblocks such that working setups keep working without sysadmin having to touch anything. Honza -- Jan Kara SUSE Labs, CR