lkml.org 
[lkml]   [2011]   [Mar]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] Fix over-zealous flush_disk when changing device size.
On Thu, Feb 17, 2011 at 04:50:57PM +1100, NeilBrown wrote:
>
> Hi Andrew (and others)
> I wonder if you would review the following for me and comment.

Please send think in this area through -fsdevel next time, thanks!

> There are two cases when we call flush_disk.
> In one, the device has disappeared (check_disk_change) so any
> data will hold becomes irrelevant.
> In the oter, the device has changed size (check_disk_size_change)
> so data we hold may be irrelevant.
>
> In both cases it makes sense to discard any 'clean' buffers,
> so they will be read back from the device if needed.

Does it? If the device has disappeared we can't read them back anyway.
If the device has resized to a smaller size the same is true about
those buffers that have gone away, and if it has resized to a larger
size invalidating anything doesn't make sense at all. I think this
area needs more love than a quick kill_dirty hackjob.

> In the former case it makes sense to discard 'dirty' buffers
> as there will never be anywhere safe to write the data. In the
> second case it *does*not* make sense to discard dirty buffers
> as that will lead to file system corruption when you simply enlarge
> the containing devices.

Doing anything like this at the buffer cache layer or inode cache layer
doesn't make any sense. If a device goes away or shrinks below the
filesystem size the filesystem simply needs to be shut down and in te
former size the admin needs to start a manual repair. Trying to do
any botch jobs in lower layer never works in practice.

For now I think the best short term fix is to simply revert commit
608aeef17a91747d6303de4df5e2c2e6899a95e8

"Call flush_disk() after detecting an online resize."


\
 
 \ /
  Last update: 2011-03-03 15:33    [W:0.142 / U:3.140 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site