Re: [patch 1/2] mm: pagecache allocation gfp fixes

[KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>]

> > Frustratingly, gfp_t is really divided into two classes of flags. One are the
> > context dependent ones (can we sleep? can we enter filesystem? block subsystem?
> > should we use some extra reserves, etc.). The other ones are the type of memory
> > required and depend on how the algorithm is implemented rather than the point
> > at which the memory is allocated (highmem? dma memory? etc).
> > 
> > Some of functions which allocate a page and add it to page cache take a gfp_t,
> > but sometimes those functions or their callers aren't really doing the right
> > thing: when allocating pagecache page, the memory type should be
> > mapping_gfp_mask(mapping). When allocating radix tree nodes, the memory type
> > should be kernel mapped (not highmem) memory. The gfp_t argument should only
> > really be needed for context dependent options.
> > 
> > This patch doesn't really solve that tangle in a nice way, but it does attempt
> > to fix a couple of bugs. find_or_create_page changes its radix-tree allocation
> > to only include the main context dependent flags in order so the pagecache
> > page may be allocated from arbitrary types of memory without affecting the
> > radix-tree. Then grab_cache_page_nowait() is changed to allocate radix-tree
> > nodes with GFP_NOFS, because it is not supposed to reenter the filesystem.
> > 
> > Filesystems should be careful about exactly what semantics they want and what
> > they get when fiddling with gfp_t masks to allocate pagecache. One should be
> > as liberal as possible with the type of memory that can be used, and same
> > for the the context specific flags.
> > 
> > Signed-off-by: Nick Piggin <npiggin@suse.de>
> 
> Looks good to me.
> 
> Reviewed-by: Pekka Enberg <penberg@cs.helsinki.fi>

me too.
	Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>




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