Re: [RFC 0/8] Cpuset aware writeback

[Christoph Lameter]

On Wed, 17 Jan 2007, Andrew Morton wrote:

> > The inode lock is not taken when the page is dirtied.
> 
> The inode_lock is taken when the address_space's first page is dirtied.  It is
> also taken when the address_space's last dirty page is cleaned.  So the place
> where the inode is added to and removed from sb->s_dirty is, I think, exactly
> the place where we want to attach and detach address_space.dirty_page_nodemask.

The problem there is that we do a GFP_ATOMIC allocation (no allocation 
context) that may fail when the first page is dirtied. We must therefore 
be able to subsequently allocate the nodemask_t in set_page_dirty(). 
Otherwise the first failure will mean that there will never be a dirty 
map for the inode/mapping.

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