Re: Antifrag patchset comments

[Hugh Dickins <hugh@veritas.com>]

On Mon, 30 Apr 2007, Mel Gorman wrote:
> On Sat, 28 Apr 2007, Christoph Lameter wrote:
> 
> > > > 11. shmem_alloc_page() shmem pages are only __GFP_RECLAIMABLE?
> > > > They can be swapped out and moved by page migration, so GFP_MOVABLE?
> > >
> > > Because they might be ramfs pages which are not movable -
> > > http://lkml.org/lkml/2006/11/24/150
> >
> > URL does not provide any useful information regarding the issue.
> 
> Not all pages allocated via shmem_alloc_page() are movable because they may
> pages for ramfs.

We seem to have a miscommunication here.

shmem_alloc_page() is static to mm/shmem.c, is used for all shm/tmpfs
data pages (unless CONFIG_TINY_SHMEM), and all those data pages may be
swapped out (while not locked in use).

ramfs pages cannot be swapped out; but shmem_alloc_page() is not used
to allocate them.  CONFIG_TINY_SHMEM uses mm/tiny-shmem.c instead of
mm/shmem.c, redirecting all shm/tmpfs requests to the simpler but
unswappable ramfs.

Hugh

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