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

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Message-ID: <20151124080734.GB1254@swordfish>
Date:	Tue, 24 Nov 2015 17:07:34 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	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 (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?

	-ss
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