From: Ross Zwisler Subject: Re: [PATCH v8 6/9] dax: add support for fsync/msync Date: Mon, 8 Feb 2016 15:06:50 -0700 Message-ID: <20160208220650.GG2343@linux.intel.com> References: <1452230879-18117-1-git-send-email-ross.zwisler@linux.intel.com> <1452230879-18117-7-git-send-email-ross.zwisler@linux.intel.com> <878u2xrjrw.fsf@openvz.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Dave Hansen , "J. Bruce Fields" , linux-mm@kvack.org, Andreas Dilger , "H. Peter Anvin" , Jeff Layton , Dan Williams , linux-nvdimm@lists.01.org, x86@kernel.org, Ingo Molnar , Matthew Wilcox , Ross Zwisler , linux-ext4@vger.kernel.org, xfs@oss.sgi.com, Alexander Viro , Thomas Gleixner , Theodore Ts'o , linux-kernel@vger.kernel.org, Jan Kara , linux-fsdevel@vger.kernel.org, Andrew Morton , Matthew Wilcox To: Dmitry Monakhov Return-path: Content-Disposition: inline In-Reply-To: <878u2xrjrw.fsf@openvz.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: xfs-bounces@oss.sgi.com Sender: xfs-bounces@oss.sgi.com List-Id: linux-ext4.vger.kernel.org On Sat, Feb 06, 2016 at 05:33:07PM +0300, Dmitry Monakhov wrote: > Ross Zwisler writes: <> > > +static int dax_radix_entry(struct address_space *mapping, pgoff_t index, > IMHO it would be sane to call that function as dax_radix_entry_insert() I think I may have actually had it named that at some point. :) I changed it because it doesn't always insert an entry - in the read case for example we insert a clean entry, and then on the following dax_pfn_mkwrite() we call back in and mark it as dirty. <> > > +/* > > + * Flush the mapping to the persistent domain within the byte range of [start, > > + * end]. This is required by data integrity operations to ensure file data is > > + * on persistent storage prior to completion of the operation. > > + */ > > +int dax_writeback_mapping_range(struct address_space *mapping, loff_t start, > > + loff_t end) > > +{ > > + struct inode *inode = mapping->host; > > + struct block_device *bdev = inode->i_sb->s_bdev; > > + pgoff_t indices[PAGEVEC_SIZE]; > > + pgoff_t start_page, end_page; > > + struct pagevec pvec; > > + void *entry; > > + int i, ret = 0; > > + > > + if (WARN_ON_ONCE(inode->i_blkbits != PAGE_SHIFT)) > > + return -EIO; > > + > > + rcu_read_lock(); > > + entry = radix_tree_lookup(&mapping->page_tree, start & PMD_MASK); > > + rcu_read_unlock(); > > + > > + /* see if the start of our range is covered by a PMD entry */ > > + if (entry && RADIX_DAX_TYPE(entry) == RADIX_DAX_PMD) > > + start &= PMD_MASK; > > + > > + start_page = start >> PAGE_CACHE_SHIFT; > > + end_page = end >> PAGE_CACHE_SHIFT; > > + > > + tag_pages_for_writeback(mapping, start_page, end_page); > > + > > + pagevec_init(&pvec, 0); > > + while (1) { > > + pvec.nr = find_get_entries_tag(mapping, start_page, > > + PAGECACHE_TAG_TOWRITE, PAGEVEC_SIZE, > > + pvec.pages, indices); > > + > > + if (pvec.nr == 0) > > + break; > > + > > + for (i = 0; i < pvec.nr; i++) { > > + ret = dax_writeback_one(bdev, mapping, indices[i], > > + pvec.pages[i]); > > + if (ret < 0) > > + return ret; > > + } > I think it would be more efficient to use batched locking like follows: > spin_lock_irq(&mapping->tree_lock); > for (i = 0; i < pvec.nr; i++) { > struct blk_dax_ctl dax[PAGEVEC_SIZE]; > radix_tree_tag_clear(page_tree, indices[i], PAGECACHE_TAG_TOWRITE); > /* It is also reasonable to merge adjacent dax > * regions in to one */ > dax[i].sector = RADIX_DAX_SECTOR(entry); > dax[i].size = (type == RADIX_DAX_PMD ? PMD_SIZE : PAGE_SIZE); > > } > spin_unlock_irq(&mapping->tree_lock); > if (blk_queue_enter(q, true) != 0) > goto error; > for (i = 0; i < pvec.nr; i++) { > rc = bdev_direct_access(bdev, dax[i]); > wb_cache_pmem(dax[i].addr, dax[i].size); > } > ret = blk_queue_exit(q, true) I guess this could be more efficient, but as Jan said in his response we're currently focused on correctness. I also wonder if it would be measurably better? In any case, Jan is right - you have to clear the TOWRITE tag only after you've flushed, and you also need to include the entry verification code from dax_writeback_one() after you grab the tree lock. Basically, I believe all the code in dax_writeback_one() is needed - this change would essentially just be inlining that code in dax_writeback_mapping_range() so you could do multiple operations without giving up a lock. _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs