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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> Precedence: bulk X-Mailing-List: linux-ext4@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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-Spam-Flag: NO X-Spam-Score: -3.80 X-Spam-Level: X-Spamd-Result: default: False [-3.80 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; MID_RHS_NOT_FQDN(0.50)[]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; MISSING_XM_UA(0.00)[]; RCPT_COUNT_TWELVE(0.00)[18]; RCVD_COUNT_THREE(0.00)[3]; FROM_HAS_DN(0.00)[]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; FROM_EQ_ENVFROM(0.00)[]; TO_DN_SOME(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FUZZY_BLOCKED(0.00)[rspamd.com]; RCVD_TLS_LAST(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.com:email,imap1.dmz-prg2.suse.org:helo,imap1.dmz-prg2.suse.org:rdns,nvidia.com:email] 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