On Tue, 30 Oct 2007 10:27:04 -0800
Badari Pulavarty <[EMAIL PROTECTED]> wrote:

> Hi,
> 
> While testing hotplug memory remove, I ran into this issue. Given a
> range of pages hotplug memory remove tries to migrate those pages.
> 
> migrate_pages() keeps failing to migrate pages containing pagecache
> pages for reiserfs files. I noticed that reiserfs doesn't have 
> ->migratepage() ops. So, fallback_migrate_page() code tries to
> do try_to_release_page(). try_to_release_page() fails to
> drop_buffers() since b_count == 1. Here is what my debug shows:
> 
>       migrate pages failed pfn 258111/flags 3f00000000801
>       bh c00000000b53f6e0 flags 110029 count 1
>       
> Any one know why the b_count == 1 and not getting dropped to zero ? 

If these are file data pages, the count is probably elevated as part of
the data=ordered tracking.  You can verify this via b_private, or just
mount data=writeback to double check.

-chris
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