linux-kernel - Re: [PATCH v3] zram: try vmalloc() after kmalloc()

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Message-ID: <20151124003500.GD3882@blaptop>
Date:	Tue, 24 Nov 2015 09:35:00 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Kyeongdon Kim <kyeongdon.kim@....com>, ngupta@...are.org,
	sergey.senozhatsky.work@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] zram: try vmalloc() after kmalloc()

On Mon, Nov 23, 2015 at 03:40:29PM -0800, Andrew Morton wrote:
> On Tue, 24 Nov 2015 08:28:57 +0900 Minchan Kim <minchan@...nel.org> wrote:
> 
> > > What's the reasoning behind the modification to the gfp flags?
> > > 
> > > It clears __GFP_FS, __GFP_IO and even __GFP_WAIT.  I suspect the latter
> > > two (at least) can be retained.  And given that vmalloc() uses
> > 
> > This function is used in swapout and fs write path so we couldn't use
> > those flags.
> 
> We can use __GFP_RECLAIM (used to be __GFP_WAIT).  That permits the
> allocation to wait for in-flight IO to complete and to reclaim clean
> pagecache.

Generally, you're right but in case of zram, it would be unfortunate.

It would be void *most of time* because it is called in reclaim context
and reclaim path bails out to avoid recursion of direct reclaim
by PF_MEMALLOC without trying reclaim.
However, the reason I said *most of time* is we has another context
the funcion could be called.

        "disksize_store"->zcomp_create

In the place, we should make sure the successful allocation to work
zram at least so that path should use another gfp.
I will work for that.

Thanks, Andrew,


> 

-- 
Kind regards,
Minchan Kim
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