On Wed, 15 Jul 2015 12:26:26 +0200 Jan Kara <jack@xxxxxxxx> wrote:
> From: Jan Kara <jack@xxxxxxx>
>
> 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 <akpm@xxxxxxxxxx>
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.
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