linux-ext4 - [PATCH 0/2] new API to allocate buffer-cache for superblock in non-movable area

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Date:	Tue, 22 Jul 2014 14:18:47 +0900
From:	Gioh Kim <gioh.kim@....com>
To:	Alexander Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>, Jan Kara <jack@...e.cz>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	"Theodore Ts'o" <tytso@....edu>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	linux-ext4@...r.kernel.org
Subject: [PATCH 0/2] new API to allocate buffer-cache for superblock in non-movable
 area

Hello,

This patch try to solve problem that a long-lasting page cache of
ext4 superblock disturbs page migration.

I've been testing CMA feature on my ARM-based platform
and found some pages for page caches cannot be migrated.
Some of them are page caches of superblock of ext4 filesystem.

Current ext4 reads superblock with sb_bread(). sb_bread() allocates page
from movable area. But the problem is that ext4 hold the page until
it is unmounted. If root filesystem is ext4 the page cannot be migrated forever.

I introduce a new API for allocating page from non-movable area.
It is useful for ext4 and others that want to hold page cache for a long time.

I have 2 patchs:

1. Patch 1/2: introduce a new API that create page cache from non-movable area
2. Patch 2/2: have ext4 use the new API to read superblock

This patchset is based on linux-next-20140717.

Thanks a lot.

Gioh Kim (2):
 fs/buffer.c: allocate buffer cache from non-movable area
 ext4: allocate buffer-cache for superblock in non-movable area

 fs/buffer.c                 |   39 ++++++++++++++++++++++++++++++++-------
 fs/ext4/super.c             |    6 +++---
 include/linux/buffer_head.h |    8 ++++++++
 3 files changed, 43 insertions(+), 10 deletions(-)

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