Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751883AbdHAJEM (ORCPT ); Tue, 1 Aug 2017 05:04:12 -0400 Received: from mx2.suse.de ([195.135.220.15]:51820 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751716AbdHAJEK (ORCPT ); Tue, 1 Aug 2017 05:04:10 -0400 Date: Tue, 1 Aug 2017 11:04:04 +0200 From: Jan Kara To: Jeff Layton Cc: Jan Kara , Andrew Morton , Al Viro , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Marcelo Tosatti Subject: Re: [PATCH] mm: remove optimizations based on i_size in mapping writeback waits Message-ID: <20170801090404.GA4215@quack2.suse.cz> References: <20170731152946.13976-1-jlayton@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170731152946.13976-1-jlayton@kernel.org> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4481 Lines: 123 On Mon 31-07-17 11:29:46, Jeff Layton wrote: > From: Jeff Layton > > Marcelo added this i_size based optimization with a patch in 2004 > (commit 765dad09b4ac in the linux-history tree): > > commit 765dad09b4ac101a32d87af2bb793c3060497d3c > Author: Marcelo Tosatti > Date: Tue Sep 7 17:51:17 2004 -0700 > > small wait_on_page_writeback_range() optimization > > filemap_fdatawait() calls wait_on_page_writeback_range() with -1 > as "end" parameter. This is not needed since we know the EOF > from the inode. Use that instead. > > There may be races here, particularly with clustered or network > filesystems. Block devices always have an i_size of 0 as well, which > makes using this with a blockdev inode sort of pointless. Well, you are not quite right here. You are correct that file_inode(file)->i_size is 0, however file->f_mapping->host->i_size is the device size and that's what will be used for filemap_fdatawait(). So that function works fine for block devices. > It also seems like a bit of a layering violation since we're operating > on an address_space here, not an inode. > > Finally, it's also questionable whether this optimization really helps > on workloads that we care about. Should we be optimizing for writeback > vs. truncate races in a codepath where we expect to wait anyway? It > doesn't seem worth the risk. > > Remove this optimization from the filemap_fdatawait codepaths. This > means that filemap_fdatawait becomes a trivial wrapper around > filemap_fdatawait_range. Agreed for all the other reasons so feel free to add: Reviewed-by: Jan Kara Honza > > Signed-off-by: Jeff Layton > --- > include/linux/fs.h | 9 +++++++-- > mm/filemap.c | 30 +----------------------------- > 2 files changed, 8 insertions(+), 31 deletions(-) > > diff --git a/include/linux/fs.h b/include/linux/fs.h > index af592ca3d509..656e04c6983e 100644 > --- a/include/linux/fs.h > +++ b/include/linux/fs.h > @@ -2538,10 +2538,15 @@ extern int invalidate_inode_pages2_range(struct address_space *mapping, > extern int write_inode_now(struct inode *, int); > extern int filemap_fdatawrite(struct address_space *); > extern int filemap_flush(struct address_space *); > -extern int filemap_fdatawait(struct address_space *); > -extern int filemap_fdatawait_keep_errors(struct address_space *mapping); > extern int filemap_fdatawait_range(struct address_space *, loff_t lstart, > loff_t lend); > +extern int filemap_fdatawait_keep_errors(struct address_space *mapping); > + > +static inline int filemap_fdatawait(struct address_space *mapping) > +{ > + return filemap_fdatawait_range(mapping, 0, LLONG_MAX); > +} > + > extern bool filemap_range_has_page(struct address_space *, loff_t lstart, > loff_t lend); > extern int __must_check file_fdatawait_range(struct file *file, loff_t lstart, > diff --git a/mm/filemap.c b/mm/filemap.c > index 394bb5e96f87..85dfe3bee324 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -512,39 +512,11 @@ EXPORT_SYMBOL(file_fdatawait_range); > */ > int filemap_fdatawait_keep_errors(struct address_space *mapping) > { > - loff_t i_size = i_size_read(mapping->host); > - > - if (i_size == 0) > - return 0; > - > - __filemap_fdatawait_range(mapping, 0, i_size - 1); > + __filemap_fdatawait_range(mapping, 0, LLONG_MAX); > return filemap_check_and_keep_errors(mapping); > } > EXPORT_SYMBOL(filemap_fdatawait_keep_errors); > > -/** > - * filemap_fdatawait - wait for all under-writeback pages to complete > - * @mapping: address space structure to wait for > - * > - * Walk the list of under-writeback pages of the given address space > - * and wait for all of them. Check error status of the address space > - * and return it. > - * > - * Since the error status of the address space is cleared by this function, > - * callers are responsible for checking the return value and handling and/or > - * reporting the error. > - */ > -int filemap_fdatawait(struct address_space *mapping) > -{ > - loff_t i_size = i_size_read(mapping->host); > - > - if (i_size == 0) > - return 0; > - > - return filemap_fdatawait_range(mapping, 0, i_size - 1); > -} > -EXPORT_SYMBOL(filemap_fdatawait); > - > static bool mapping_needs_writeback(struct address_space *mapping) > { > return (!dax_mapping(mapping) && mapping->nrpages) || > -- > 2.13.3 > -- Jan Kara SUSE Labs, CR