linux-kernel - Re: [PATCH v2] zram: Prevent page allocation failure during zcomp_strm

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Message-ID: <20151123031400.GA7449@swordfish>
Date:	Mon, 23 Nov 2015 12:14:00 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Kyeongdon Kim <kyeongdon.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>, ngupta@...are.org,
	sergey.senozhatsky.work@...il.com, linux-kernel@...r.kernel.org,
	sergey.senozhatsky@...il.com
Subject: Re: [PATCH v2] zram: Prevent page allocation failure during
 zcomp_strm_alloc

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
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