From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Fri, 22 Jan 2016 09:01:17 -0700 From: Ross Zwisler To: Jan Kara Cc: Ross Zwisler , linux-kernel@vger.kernel.org, Alexander Viro , Andrew Morton , Dan Williams , Dave Chinner , Jan Kara , Matthew Wilcox , linux-fsdevel@vger.kernel.org, linux-nvdimm@lists.01.org Subject: Re: [PATCH v2 4/5] dax: fix PMD handling for fsync/msync Message-ID: <20160122160117.GB22112@linux.intel.com> References: <1453398364-22537-1-git-send-email-ross.zwisler@linux.intel.com> <1453398364-22537-5-git-send-email-ross.zwisler@linux.intel.com> <20160122151141.GM16898@quack.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160122151141.GM16898@quack.suse.cz> Sender: linux-kernel-owner@vger.kernel.org List-ID: On Fri, Jan 22, 2016 at 04:11:41PM +0100, Jan Kara wrote: > On Thu 21-01-16 10:46:03, Ross Zwisler wrote: > > Fix the way that DAX PMD radix tree entries are handled. With this patch > > we now check to see if a PMD entry exists in the radix tree on write, even > > if we are just trying to insert a PTE. If it exists, we dirty that instead > > of inserting our own PTE entry. > > > > Fix a bug in the PMD path in dax_writeback_mapping_range() where we were > > previously passing a loff_t into radix_tree_lookup instead of a pgoff_t. > > Ah, good catch! > > > Account for the fact that multiple fsync/msync operations may be happening > > at the same time and don't flush entries that are beyond end_index. > > > > Signed-off-by: Ross Zwisler > > Just one nit below. You can add: > > Reviewed-by: Jan Kara > > > --- > > fs/dax.c | 39 +++++++++++++++++++++++++++------------ > > 1 file changed, 27 insertions(+), 12 deletions(-) > > > > diff --git a/fs/dax.c b/fs/dax.c > > index 55ae394..afacc30 100644 > > --- a/fs/dax.c > > +++ b/fs/dax.c > ... > > @@ -460,31 +468,33 @@ int dax_writeback_mapping_range(struct address_space *mapping, loff_t start, > > { > > struct inode *inode = mapping->host; > > struct block_device *bdev = inode->i_sb->s_bdev; > > + pgoff_t start_index, end_index, pmd_index; > > pgoff_t indices[PAGEVEC_SIZE]; > > - pgoff_t start_page, end_page; > > struct pagevec pvec; > > - void *entry; > > + bool done = false; > > int i, ret = 0; > > + void *entry; > > > > if (WARN_ON_ONCE(inode->i_blkbits != PAGE_SHIFT)) > > return -EIO; > > > > + start_index = start >> PAGE_CACHE_SHIFT; > > + end_index = end >> PAGE_CACHE_SHIFT; > > + pmd_index = DAX_PMD_INDEX(start_index); > > + > > rcu_read_lock(); > > - entry = radix_tree_lookup(&mapping->page_tree, start & PMD_MASK); > > + entry = radix_tree_lookup(&mapping->page_tree, pmd_index); > > 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; > > + if (RADIX_DAX_TYPE(entry) == RADIX_DAX_PMD) > > Don't you miss a check that entry != NULL? I agree that RADIX_DAX_TYPE(NULL) > is != from RADIX_DAX_PMD so it works as desired but it looks a bit > dangerous. Yea, the initial version had a NULL check first, but I realized I could optimize it out and make things simpler since RADIX_DAX_TYPE() just looked at the value of 'entry' and never treated it like a pointer (because to us, it isn't a pointer). I will add it back if you think that not having it may confuse the reader.