Re: [PATCH v2] zram: Prevent page allocation failure during zcomp_strm_alloc

[Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>]

Hello,

On (11/23/15 11:15), Minchan Kim wrote:
[..]
> >  static void *zcomp_lz4_create(void)
> >  {
> > -	return kzalloc(LZ4_MEM_COMPRESS, GFP_KERNEL);
> > +	void *ret;
> > +
> > +	ret = kzalloc(LZ4_MEM_COMPRESS,
> > +			__GFP_NORETRY|__GFP_NOWARN|__GFP_NOMEMALLOC);
> > +	if (!ret)
> > +		ret = vzalloc(LZ4_MEM_COMPRESS);
> 
> One thing I feel bad smell is that call vzalloc with GFP_KERNEL.
> This function can be called in direct reclaim path with holding
> fs lock and GFP_KERNEL can enter recursive reclaim path so
> lockdep would complain theoretically if I don't miss something.
> 

yes, GFP_KERNEL looks a bit fragile to me too. And may be zcomp_strm_alloc()
and comp->backend->create() deserve GFP_NOFS. I believe I sent a patch doing
this a while ago: https://lkml.org/lkml/2015/6/16/465

> If it is true, we should fix several allocation flags in
> zcomp_strm_alloc. I just want to record this warning for the future
> in this thread so someone who is finding for the contribution
> material will prove and fix it. :)

I can re-send the patch.

And, in case if you missed it, what's your opinion on the idea of
reducing ->max_strm if we can't allocate new streams. Here:
http://marc.info/?l=linux-kernel&m=144798049429861

	-ss