Re: [PATCH 2] mm/kvmalloc: do not call kmalloc for size > KMALLOC_MAX_SIZE

[Konstantin Khlebnikov]

On 05.11.2018 16:03, Vlastimil Babka wrote:
> On 11/1/18 11:09 AM, Konstantin Khlebnikov wrote:
> > Allocations over KMALLOC_MAX_SIZE could be served only by vmalloc.
> >
> > Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
>
> Makes sense regardless of warnings stuff.
>
> Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
>
> But it must be moved below the GFP_KERNEL check!

But kmalloc cannot handle it regardless of GFP.

Ok maybe write something like this

if (size > KMALLOC_MAX_SIZE) {
	if (WARN_ON_ONCE((flags & GFP_KERNEL) != GFP_KERNEL)
		return NULL;
	goto do_vmalloc;
}

or fix that uncertainty right in vmalloc

For now comment in vmalloc declares

 *	Any use of gfp flags outside of GFP_KERNEL should be consulted
 *	with mm people.

=)

> > ---
> >   mm/util.c |    4 ++++
> >   1 file changed, 4 insertions(+)
> >
> > diff --git a/mm/util.c b/mm/util.c
> > index 8bf08b5b5760..f5f04fa22814 100644
> > --- a/mm/util.c
> > +++ b/mm/util.c
> > @@ -392,6 +392,9 @@ void *kvmalloc_node(size_t size, gfp_t flags, int node)
> >   	gfp_t kmalloc_flags = flags;
> >   	void *ret;
> >   
> > +	if (size > KMALLOC_MAX_SIZE)
> > +		goto fallback;
> > +
> >   	/*
> >   	 * vmalloc uses GFP_KERNEL for some internal allocations (e.g page tables)
> >   	 * so the given set of flags has to be compatible.
> > @@ -422,6 +425,7 @@ void *kvmalloc_node(size_t size, gfp_t flags, int node)
> >   	if (ret || size <= PAGE_SIZE)
> >   		return ret;
> >   
> > +fallback:
> >   	return __vmalloc_node_flags_caller(size, node, flags,
> >   			__builtin_return_address(0));
> >   }