linux-kernel - Re: [PATCH 2/3] zram: try vmalloc() after kmalloc()

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Message-ID: <20151124081426.GB32717@blaptop>
Date:	Tue, 24 Nov 2015 17:14:26 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Kyeongdon Kim <kyeongdon.kim@....com>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [PATCH 2/3] zram: try vmalloc() after kmalloc()

On Tue, Nov 24, 2015 at 05:07:34PM +0900, Sergey Senozhatsky wrote:
> On (11/24/15 16:57), Minchan Kim wrote:
> [..]
> > > hm, ok, may be.
> > > but the question whether we want to waste pages on additional streams
> > > (especially, e.g. if we already have, say, 10 streams) is still valid.
> > > a more intuitive here is to release some unneeded streams, not to increase
> > > our pressure allocating new ones. well, at least it seems to be so.
> > > those pages can be used by zsmalloc, for example.
> > 
> > I think your claim make sense if the failure comes from high memory
> > pressure but order-3 alloc failure even if there are lots of order-0
> > free pages in my experience is easy to encouter so I think it doesn't
> > mean memory pressure but just memory fragmentation.
> 
> hm, yes, fragmentation can be one of the reasons.
> 
> > > > > ... and add GFP_NOIO to both kzalloc() and __vmalloc().
> > > > 
> > > > I can add it. The harmness is really ignorable but as I mentioned
> > > > at reply of Andrew, what's the benefit with GFP_NOIO?
> > > > We couldn't make forward progress with __GFP_RECLAIM in reclaim
> > > > context.
> > > 
> > > aha, I probably missed that out.
> > > (well, and, technically, things can change).
> > 
> > My speaking came from MM internal knowledge so I accept your concern.
> > if you prefer like GFP_NOIO, I will use it in next spin which
> > makes reader less confused.
> 
> ok, I found your comment
> 
> : 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.
> 
> well, we also allocate streams from sysfs store and during 'normal' IO
> (e.g. from fs). wouldn't GFP_NOIO be helpful there?

In [3/3], I used GFP_KERNEL for sysfs_store but with FS, you're
absoultely right. I have no reason not to use GFP_NOIO in there.
Thanks for the review!

> 
> 	-ss

-- 
Kind regards,
Minchan Kim
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