On Tue, 2007-10-30 at 18:58 -0400, Chris Mason wrote:

On Tue, 30 Oct 2007 13:54:05 -0800
Badari Pulavarty [off-list ref] wrote:

quoted

On Tue, 2007-10-30 at 13:54 -0400, Chris Mason wrote:

quoted

On Tue, 30 Oct 2007 10:27:04 -0800
Badari Pulavarty [off-list ref] wrote:

quoted

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,

That was my first assumption. But after looking at
reiserfs_releasepage (), realized that it would do reiserfs_free_jh()
and clears the b_private. I couldn't easily find out who has the ref.
against this bh.

bh c00000000bdaaf00 flags 110029 count 1 private 0

If I'm reading this correctly the buffer is BH_Lock | BH_Req, perhaps
it is currently under IO?

The page isn't locked, but data=ordered does IO directly on the buffer
heads, without taking the page lock.

The easy way to narrow our search is to try without data=ordered, it is
certainly complicating things.

I tried data=writeback mode and it didn't help :(

unable to release the page 262070
bh c0000000211b9408 flags 110029 count 1 private 0
unable to release the page 262098
bh c000000020ec9198 flags 110029 count 1 private 0
memory offlining 3f000 to 40000 failed

# cat /etc/mtab
/dev/sda3 / reiserfs rw,data=writeback 0 0
proc /proc proc rw 0 0
tmpfs /dev/shm tmpfs rw 0 0
devpts /dev/pts devpts rw,mode=0620,gid=5 0 0

Thanks,
Badari


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