From: Jan Kara Subject: Re: [PATCH v8 2/9] dax: fix conversion of holes to PMDs Date: Tue, 12 Jan 2016 10:44:51 +0100 Message-ID: <20160112094451.GS6262@quack.suse.cz> References: <1452230879-18117-1-git-send-email-ross.zwisler@linux.intel.com> <1452230879-18117-3-git-send-email-ross.zwisler@linux.intel.com> 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 , 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: Ross Zwisler Return-path: Content-Disposition: inline In-Reply-To: <1452230879-18117-3-git-send-email-ross.zwisler@linux.intel.com> 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 Thu 07-01-16 22:27:52, Ross Zwisler wrote: > When we get a DAX PMD fault for a write it is possible that there could be > some number of 4k zero pages already present for the same range that were > inserted to service reads from a hole. These 4k zero pages need to be > unmapped from the VMAs and removed from the struct address_space radix tree > before the real DAX PMD entry can be inserted. > > For PTE faults this same use case also exists and is handled by a > combination of unmap_mapping_range() to unmap the VMAs and > delete_from_page_cache() to remove the page from the address_space radix > tree. > > For PMD faults we do have a call to unmap_mapping_range() (protected by a > buffer_new() check), but nothing clears out the radix tree entry. The > buffer_new() check is also incorrect as the current ext4 and XFS filesystem > code will never return a buffer_head with BH_New set, even when allocating > new blocks over a hole. Instead the filesystem will zero the blocks > manually and return a buffer_head with only BH_Mapped set. > > Fix this situation by removing the buffer_new() check and adding a call to > truncate_inode_pages_range() to clear out the radix tree entries before we > insert the DAX PMD. > > Signed-off-by: Ross Zwisler > Reported-by: Dan Williams > Tested-by: Dan Williams Just two nits below. Nothing serious so you can add: Reviewed-by: Jan Kara > --- > fs/dax.c | 20 ++++++++++---------- > 1 file changed, 10 insertions(+), 10 deletions(-) > > diff --git a/fs/dax.c b/fs/dax.c > index 513bba5..5b84a46 100644 > --- a/fs/dax.c > +++ b/fs/dax.c > @@ -589,6 +589,7 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address, > bool write = flags & FAULT_FLAG_WRITE; > struct block_device *bdev; > pgoff_t size, pgoff; > + loff_t lstart, lend; > sector_t block; > int result = 0; > > @@ -643,15 +644,13 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address, > goto fallback; > } > > - /* > - * If we allocated new storage, make sure no process has any > - * zero pages covering this hole > - */ > - if (buffer_new(&bh)) { > - i_mmap_unlock_read(mapping); > - unmap_mapping_range(mapping, pgoff << PAGE_SHIFT, PMD_SIZE, 0); > - i_mmap_lock_read(mapping); > - } > + /* make sure no process has any zero pages covering this hole */ > + lstart = pgoff << PAGE_SHIFT; > + lend = lstart + PMD_SIZE - 1; /* inclusive */ > + i_mmap_unlock_read(mapping); Just a nit but is there reason why we grab i_mmap_lock_read(mapping) only to release it a few lines below? The bh checks inside the locked region don't seem to rely on i_mmap_lock... > + unmap_mapping_range(mapping, lstart, PMD_SIZE, 0); > + truncate_inode_pages_range(mapping, lstart, lend); These two calls can be shortened as: truncate_pagecache_range(inode, lstart, lend); Honza -- Jan Kara SUSE Labs, CR _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs