Re: [PATCH] mm: use vmalloc fallback path for certain memcg allocations

[Heiko Carstens <heiko.carstens@de.ibm.com>]

On Mon, Dec 05, 2016 at 06:23:26AM +0100, Michal Hocko wrote:
> > > 
> > > 	ret = kzalloc(size, gfp_mask);
> > > 	if (ret)
> > > 		return ret;
> > > 	return vzalloc(size);
> > > 
> > 
> > > I also do not like memcg_alloc helper name. It suggests we are
> > > allocating a memcg while it is used for cache arrays and slab LRUS.
> > > Anyway this pattern is quite widespread in the kernel so I would simply
> > > suggest adding kvmalloc function instead.
> > 
> > Agreed, it would be nice to have a generic call.
> > I would suggest an impl. like this:
> > 
> > void *kvmalloc(size_t size)
> 
> gfp_t gfp_mask should be a parameter as this should be a generic helper.
> 
> > {
> > 	gfp_t gfp_mask = GFP_KERNEL;
> 
> 
> > 	void *ret;
> > 
> >  	if (size > PAGE_SIZE)
> >  		gfp_mask |= __GFP_NORETRY | __GFP_NOWARN;
> > 
> > 
> > 	if (size <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER)) {
> > 		ret = kzalloc(size, gfp_mask);
> > 		if (ret)
> > 			return ret;
> > 	}
> 
> No, please just do as suggested above. Tweak the gfp_mask for higher
> order requests and do kmalloc first with vmalloc as a  fallback.

You may simply use the slightly different and open-coded variant within
fs/seq_file.c:seq_buf_alloc(). That one got a lot of testing in the
meantime...

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