On Tue, 16 Jan 2007, Andrew Morton wrote:

Do what blockdevs do: limit the number of in-flight requests (Peter's
recent patch seems to be doing that for us) (perhaps only when PF_MEMALLOC
is in effect, to keep Trond happy) and implement a mempool for the NFS
request critical store.  Additionally:

- we might need to twiddle the NFS gfp_flags so it doesn't call the
  oom-killer on failure: just return NULL.

- consider going off-cpuset for critical allocations.  It's better than
  going oom.  A suitable implementation might be to ignore the caller's
  cpuset if PF_MEMALLOC.  Maybe put a WARN_ON_ONCE in there: we prefer that
  it not happen and we want to know when it does.

Given the intermediate  layers (network, additional gizmos (ip over xxx) 
and the network cards) that will not be easy.

btw, regarding the per-address_space node mask: I think we should free it
when the inode is clean (!mapping_tagged(PAGECACHE_TAG_DIRTY)).  Chances
are, the inode will be dirty for 30 seconds and in-core for hours.  We
might as well steal its nodemask storage and give it to the next file which
gets written to.  A suitable place to do all this is in
__mark_inode_dirty(I_DIRTY_PAGES), using inode_lock to protect
address_space.dirty_page_nodemask.

The inode lock is not taken when the page is dirtied. The tree_lock
is already taken when the mapping is dirtied and so I used that to
avoid races adding and removing pointers to nodemasks from the address 
space.

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