From: Andrew Morton Subject: Re: [PATCH 2/3] fs: Remove ext3 filesystem driver Date: Wed, 15 Jul 2015 09:58:22 -0700 Message-ID: <20150715095822.f994bc58.akpm@linux-foundation.org> References: <1436955987-7305-1-git-send-email-jack@suse.com> <1436955987-7305-3-git-send-email-jack@suse.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, LKML , Andreas Dilger , Jens Axboe , Ted Tso , Jan Kara To: Jan Kara Return-path: In-Reply-To: <1436955987-7305-3-git-send-email-jack@suse.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On Wed, 15 Jul 2015 12:26:26 +0200 Jan Kara wrote: > From: Jan Kara > > The functionality of ext3 is fully supported by ext4 driver. Major > distributions (SUSE, RedHat) already use ext4 driver to handle ext3 > filesystems for quite some time. There is some ugliness in mm resulting > from jbd cleaning buffers in a dirty page without cleaning page dirty > bit and also support for buffer bouncing in the block layer when stable > pages are required is there only because of jbd. So let's remove the > ext3 driver. Does this imply that ext4 doesn't do the secretly-clean-the-page-via-buffers thing? If so, how? The comment in shrink_page_list() says the blockdev mapping will do this as well, although I can't imagine how - there's no means of getting to those buffer_heads except via the page. So maybe the "even if the page is PageDirty()" is no longer true. It was added by: commit 493f4988d640a73337df91f2c63e94c78ecd5e97 Author: Andrew Morton Date: Mon Jun 17 20:20:53 2002 -0700 [PATCH] allow GFP_NOFS allocators to perform swapcache writeout One weakness which was introduced when the buffer LRU went away was that GFP_NOFS allocations became equivalent to GFP_NOIO. Because all writeback goes via writepage/writepages, which requires entry into the filesystem. However now that swapout no longer calls bmap(), we can honour GFP_NOFS's intent for swapcache pages. So if the allocation request specifies __GFP_IO and !__GFP_FS, we can wait on swapcache pages and we can perform swapcache writeout. This should strengthen the VM somewhat. I wonder what I was thinking. Also, what's the status of ext4's data=journal? It's the hardest ext3 mode for the rest of the kernel to support and I suspect hardly anyone uses it. > 46 files changed, 54 insertions(+), 28109 deletions(-) Heroic.