On Thu 14-08-14 14:26:10, Andrew Morton wrote: > On Thu, 14 Aug 2014 14:12:17 +0900 Gioh Kim <gioh.kim@xxxxxxx> wrote: > > > This patch try to solve problem that a long-lasting page caches of > > ext4 superblock and journaling of superblock disturb page migration. > > > > I've been testing CMA feature on my ARM-based platform > > and found that two page caches cannot be migrated. > > They are page caches of superblock of ext4 filesystem and its journaling data. > > > > Current ext4 reads superblock with sb_bread() that 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. > > And also the journaling data for the superblock cannot be migreated. > > > > I introduce a new API for allocating page cache from non-movable area. > > It is useful for ext4/ext3 and others that want to hold page cache for a long time. > > All seems reasonable to me. The additional overhead in buffer.c from > additional function arguments is regrettable but I don't see a > non-hacky alternative. > > One vital question which the changelog doesn't really address (it > should): how important is this patch? Is your test system presently > "completely dead in the water utterly unusable" or "occasionally not > quite as good as it could be". Somewhere in between? I would be also interested in how much these patches make things better. Because I would expect all metadata that is currently journalled to be unmovable as well. Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
