linux-kernel - Re: [PATCH v3 2/2] zram: try vmalloc() after kmalloc()

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Date:	Tue, 1 Dec 2015 14:16:52 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	"kyeongdon.kim" <kyeongdon.kim@....com>,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [PATCH v3 2/2] zram: try vmalloc() after kmalloc()

On (12/01/15 13:55), Minchan Kim wrote:
[..]
> To clear my opinion,
> 
> lzo_create(gfp_t flags)
> {
>         void * ret = kmalloc(LZO1X_MEM_COMPRESS, flags);
>         if (!ret)
>                 ret = vmalloc(LZO1X_MEM_COMPRESS, flasgs | GFP_NOMEMALLOC);
>         return ret;
> }

ah, ok, I see. I've a question.

we had
	kmalloc(f | __GFP_NOMEMALLOC)
	__vmalloc(f | __GFP_NOMEMALLOC)

which produced high failure rates for both kmalloc() and __vmalloc()

test #1

> > > log message :
[..]
> > > [  352.230608][0] zcomp_lz4_create: 32: ret =           (null)
> > > [  352.230619][0] zcomp_lz4_create: 38: ret =           (null)
> > > [  352.230888][0] zcomp_lz4_create: 32: ret =           (null)
> > > [  352.230902][0] zcomp_lz4_create: 38: ret =           (null)
> > > [  352.231406][0] zcomp_lz4_create: 32: ret = ffffffc002088000
> > > [  352.234024][0] zcomp_lz4_create: 32: ret =           (null)
> > > [  352.234060][0] zcomp_lz4_create: 38: ret =           (null)
> > > [  352.234359][0] zcomp_lz4_create: 32: ret =           (null)
[..]
> > > [  352.234384][0] zcomp_lz4_create: 38: ret =           (null)
> > > [  352.234618][0] zcomp_lz4_create: 32: ret =           (null)
> > > [  352.234639][0] zcomp_lz4_create: 38: ret =           (null)
> > > [  352.234667][0] zcomp_lz4_create: 32: ret =           (null)
> > > [  352.235179][0] zcomp_lz4_create: 38: ret = ffffff80016a4000



Kyeongdon, do I understand correctly, that for the second test you
removed '__GFP_NOMEMALLOC' from both kmalloc() and __vmalloc()?

iow:
	kmalloc(f & ~__GFP_NOMEMALLOC)
	vmalloc(f & ~__GFP_NOMEMALLOC)

test #2 : almost always failing kmalloc() and !NULL __vmalloc()

> > > log message :
> > > <4>[ 2288.954934][0] KDKIM: zcomp_lz4_create: 24: ret =           (null)
> > > <4>[ 2288.954972][0] KDKIM: zcomp_lz4_create: 30: ret = ffffff800287e000
> > > ..<snip>..
> > > <4>[ 2289.092411][0] KDKIM: zcomp_lz4_create: 24: ret =           (null)
> > > <4>[ 2289.092546][0] KDKIM: zcomp_lz4_create: 30: ret = ffffff80028b5000
> > > ..<snip>..
> > > <4>[ 2289.135628][0] KDKIM: zcomp_lz4_create: 24: ret =           (null)
> > > <4>[ 2289.135642][0] KDKIM: zcomp_lz4_create: 24: ret =           (null)
> > > <4>[ 2289.135729][0] KDKIM: zcomp_lz4_create: 30: ret = ffffff80028be000
> > > <4>[ 2289.135732][0] KDKIM: zcomp_lz4_create: 30: ret = ffffff80028c7000


if this is the case (__GFP_NOMEMALLOC removed from both kmalloc and __vmalloc),
then proposed

	kmalloc(f & ~__GFP_NOMEMALLOC)
	__vmalloc(f | __GFP_NOMEMALLOC)


can be very close to 'test #1 && test #2':

	kmalloc() fails (as in test #2)
	__vmalloc() fails (as in test #1)

isn't it?

	-ss
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