Block device swamping disk cache

[marcus hall]

I am having problems writing a filesystem image to a device file.

I am running an arm version of the 2.5.59 kernel.

Writing the data to the device file eventually caused ps.nr_dirty to exceed
dirty_thresh in balance_dirty_pages(), yet when writeback_inodes() scans
all the superblocks, the inodes that it finds are all marked as memory_backed
(they are on a ramdisk), and the inode for the block device file doesn't
show up.

I did not see any place where mark_inode_dirty() gets called for the block
device..  Is there some other mechanism for flushing the disk cache allocated
to the device?  I end up with balance_dirty_pages() looping forever.

Just for grins, I added a call to mark_inode_dirty() in blkdev_commit_write()
(similar to generic_commit_write()), but this had no effect that I could
notice.  I did note that in blkdev_commit_write(), if I look at
file->f_dentry->d_inode, I see the inode form the /dev filesystem, yet
page->mapping->host is a different inode!  I don't know if this is a
problem or not, but it did surprise me..

Anyhow, is this a known issue with 2.5.59?  How is the disk cache allocated
to a block device supposed to get flushed?

Thanks!

Marcus Hall
marcus@xxxxxxxxxx
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