From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758427AbaDIJ0l (ORCPT ); Wed, 9 Apr 2014 05:26:41 -0400 Received: from cantor2.suse.de ([195.135.220.15]:50320 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758121AbaDIJ0k (ORCPT ); Wed, 9 Apr 2014 05:26:40 -0400 Date: Wed, 9 Apr 2014 11:26:35 +0200 From: Jan Kara To: Matthew Wilcox Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, willy@linux.intel.com Subject: Re: [PATCH v7 08/22] Replace xip_truncate_page with dax_truncate_page Message-ID: <20140409092635.GB32103@quack.suse.cz> References: <20140408221759.GD26019@quack.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140408221759.GD26019@quack.suse.cz> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 09-04-14 00:17:59, Jan Kara wrote: > On Sun 23-03-14 15:08:34, Matthew Wilcox wrote: > > +/** > > + * dax_truncate_page - handle a partial page being truncated in a DAX file > > + * @inode: The file being truncated > > + * @from: The file offset that is being truncated to > > + * @get_block: The filesystem method used to translate file offsets to blocks > > + * > > + * Similar to block_truncate_page(), this function can be called by a > > + * filesystem when it is truncating an DAX file to handle the partial page. > > + * > > + * We work in terms of PAGE_CACHE_SIZE here for commonality with > > + * block_truncate_page(), but we could go down to PAGE_SIZE if the filesystem > > + * took care of disposing of the unnecessary blocks. Even if the filesystem > > + * block size is smaller than PAGE_SIZE, we have to zero the rest of the page > > + * since the file might be mmaped. > Well, DAX mmap support pretty much relies on PAGE_CACHE_SIZE == block > size (we cannot really map only a part of a physical page directly...). So > the comment seems somewhat misleading. I thought about this for a while and classical IO, truncation etc. could easily work for blocksize < pagesize. And for mmap() you could just use pagecache. Not sure if it's worth the complications though. Anyway we should decide whether we don't care about blocksize < PAGE_CACHE_SIZE at all, or whether we try to make things which can work reasonably easily functional. In that case dax_truncate_page() needs some tweaking because it currently assumes blocksize == PAGE_CACHE_SIZE. Honza > -- > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Jan Kara SUSE Labs, CR