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Fri, 12 Apr 2024 15:22:08 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id qVT4JKBRGWa1BAAAD6G6ig (envelope-from ); Fri, 12 Apr 2024 15:22:08 +0000 Received: by quack3.suse.cz (Postfix, from userid 1000) id 2B0A8A071E; Fri, 12 Apr 2024 17:22:08 +0200 (CEST) Date: Fri, 12 Apr 2024 17:22:08 +0200 From: Jan Kara To: Alistair Popple Cc: linux-mm@kvack.org, david@fromorbit.com, dan.j.williams@intel.com, jhubbard@nvidia.com, rcampbell@nvidia.com, willy@infradead.org, jgg@nvidia.com, linux-fsdevel@vger.kernel.org, jack@suse.cz, djwong@kernel.org, hch@lst.de, david@redhat.com, ruansy.fnst@fujitsu.com, nvdimm@lists.linux.dev, linux-xfs@vger.kernel.org, linux-ext4@vger.kernel.org, jglisse@redhat.com Subject: Re: [RFC 04/10] fs/dax: Don't track page mapping/index Message-ID: <20240412152208.m25mjo3xjfyawcaj@quack3> References: <322065d373bb6571b700dba4450f1759b304644a.1712796818.git-series.apopple@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <322065d373bb6571b700dba4450f1759b304644a.1712796818.git-series.apopple@nvidia.com> X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 74F51180010 X-Stat-Signature: 584d5zmcu5xjc7uudy7j9w9b7c68frpa X-Rspam-User: X-HE-Tag: 1712935330-833781 X-HE-Meta: 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 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: List-Subscribe: List-Unsubscribe: On Thu 11-04-24 10:57:25, Alistair Popple wrote: > The page->mapping and page->index fields are normally used by the > pagecache and rmap for looking up virtual mappings of pages. FS DAX > implements it's own kind of page cache and rmap look ups so these > fields are unnecessary. They are currently only used to detect > error/warning conditions which should never occur. > > A future change will change the way shared mappings are detected by > doing normal page reference counting instead, so remove the > unnecessary checks. > > Signed-off-by: Alistair Popple ... > -/* > - * When it is called in dax_insert_entry(), the shared flag will indicate that > - * whether this entry is shared by multiple files. If so, set the page->mapping > - * PAGE_MAPPING_DAX_SHARED, and use page->share as refcount. > - */ > -static void dax_associate_entry(void *entry, struct address_space *mapping, > - struct vm_area_struct *vma, unsigned long address, bool shared) > -{ > - unsigned long size = dax_entry_size(entry), pfn, index; > - int i = 0; > - > - if (IS_ENABLED(CONFIG_FS_DAX_LIMITED)) > - return; > - > - index = linear_page_index(vma, address & ~(size - 1)); > - for_each_mapped_pfn(entry, pfn) { > - struct page *page = pfn_to_page(pfn); > - > - if (shared) { > - dax_page_share_get(page); > - } else { > - WARN_ON_ONCE(page->mapping); > - page->mapping = mapping; > - page->index = index + i++; > - } > - } > -} Hum, but what about existing uses of folio->mapping and folio->index in fs/dax.c? AFAICT this patch breaks them. What am I missing? How can this ever work? Honza -- Jan Kara SUSE Labs, CR