Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1655959

Re: [PATCH 1/9] mm: introduce kv[mz]alloc helpers

Show all headers | View raw

On Fri 02-06-17 07:17:22, Sasha Levin wrote:
> On Mon, Mar 06, 2017 at 11:30:24AM +0100, Michal Hocko wrote:
> > +void *kvmalloc_node(size_t size, gfp_t flags, int node)
> > +{
> > +	gfp_t kmalloc_flags = flags;
> > +	void *ret;
> > +
> > +	/*
> > +	 * vmalloc uses GFP_KERNEL for some internal allocations (e.g page tables)
> > +	 * so the given set of flags has to be compatible.
> > +	 */
> > +	WARN_ON_ONCE((flags & GFP_KERNEL) != GFP_KERNEL);
> 
> Hm, there are quite a few locations in the kernel that do something like:
> 
> 	__vmalloc(len, GFP_NOFS, PAGE_KERNEL);
> 
> According to your patch, vmalloc can't really do GFP_NOFS, right?

Yes. It is quite likely that they will just work because the hardcoded
GFP_KERNEL inside the vmalloc path is in unlikely paths (page table
allocations for example) but yes they are broken. I didn't convert some
places which opencode the kvmalloc with GFP_NOFS because I strongly
_believe_ that the GFP_NOFS should be revisited, checked whether it is
needed, documented if so and then memalloc_nofs__{save,restore} be used
for the scope which is reclaim recursion unsafe. This would turn all
those vmalloc users to the default GFP_KERNEL and still do the right
thing.
-- 
Michal Hocko
SUSE Labs

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Re: [PATCH 1/9] mm: introduce kv[mz]alloc helpers "Levin, Alexander (Sasha Levin)" <alexander.levin@verizon.com> - 2017-06-02 09:20 +0200
  Re: [PATCH 1/9] mm: introduce kv[mz]alloc helpers Michal Hocko <mhocko@kernel.org> - 2017-06-02 09:30 +0200
    Re: [PATCH 1/9] mm: introduce kv[mz]alloc helpers "Levin, Alexander (Sasha Levin)" <alexander.levin@verizon.com> - 2017-06-02 09:50 +0200
      Re: [PATCH 1/9] mm: introduce kv[mz]alloc helpers Michal Hocko <mhocko@kernel.org> - 2017-06-02 10:00 +0200

csiph-web