Re: [PATCH 3/8] ext4: Warn if direct reclaim tries to writeback pages

[Christoph Hellwig <hch@xxxxxxxxxxxxx>]

On Wed, Aug 03, 2011 at 04:00:19PM +0200, Johannes Weiner wrote:
> > That said, in my current revision of the series, I've dropped these
> > patches altogether as page migration should be able to trigger the same
> > warnings but be called from paths that are of less concern for stack
> > overflows (or at the very least be looked at as a separate series).
> 
> Doesn't this only apply to btrfs which has no own .migratepage aop for
> file pages?  The others use buffer_migrate_page.
> 
> But if you dropped them anyway, it does not matter :)

Note that the mid-term plan is to kill ->writepage as an address space
method.  Besides the usage from reclaim as as callbacks to
write_cache_pages and write_one_page (which can be made explicit
arguments) the only remaining user is the above mentioned fallback.

Josef, any chance you could switch btrfs over to implement a proper
->migratepage?