On Tue, Mar 07, 2017 at 03:08:45PM -0800, Andrew Morton wrote: > On Tue, 7 Mar 2017 15:10:20 +0100 Michal Hocko <mho...@kernel.org> wrote: > > > __vmalloc* allows users to provide gfp flags for the underlying > > allocation. This API is quite popular > > $ git grep "=[[:space:]]__vmalloc\|return[[:space:]]*__vmalloc" | wc -l > > 77 > > > > the only problem is that many people are not aware that they really want > > to give __GFP_HIGHMEM along with other flags because there is really no > > reason to consume precious lowmemory on CONFIG_HIGHMEM systems for pages > > which are mapped to the kernel vmalloc space. About half of users don't > > use this flag, though. This signals that we make the API unnecessarily > > too complex. > > > > This patch simply uses __GFP_HIGHMEM implicitly when allocating pages to > > be mapped to the vmalloc space. Current users which add __GFP_HIGHMEM > > are simplified and drop the flag. > > hm. What happens if a caller wants only lowmem pages? Drivers do > weird stuff...
That's not something drivers actually want ... they might want "only pages under 4GB", which is why we have vmalloc_32(), but drivers don't really care where the HIGHMEM / LOWMEM split is. I suppose we might find some cases where drivers have mistakenly used vmalloc() and "got away with it".
