From: Andrew Morton <akpm@linux-foundation.org>
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Namhyung Kim <namhyung@gmail.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm: cleanup gfp_zone()
Date: Tue, 28 Sep 2010 14:45:18 -0700 [thread overview]
Message-ID: <20100928144518.0eaf1099.akpm@linux-foundation.org> (raw)
In-Reply-To: <20100928214141.GG19804@ZenIV.linux.org.uk>
On Tue, 28 Sep 2010 22:41:42 +0100
Al Viro <viro@ZenIV.linux.org.uk> wrote:
> On Tue, Sep 28, 2010 at 02:32:39PM -0700, Andrew Morton wrote:
> > > +#define ZT_SHIFT(gfp) ((__force int) (gfp) * ZONES_SHIFT)
> > > #define GFP_ZONE_TABLE ( \
> > > - (ZONE_NORMAL << 0 * ZONES_SHIFT) \
> > > - | (OPT_ZONE_DMA << __GFP_DMA * ZONES_SHIFT) \
> > > - | (OPT_ZONE_HIGHMEM << __GFP_HIGHMEM * ZONES_SHIFT) \
> > > - | (OPT_ZONE_DMA32 << __GFP_DMA32 * ZONES_SHIFT) \
> > > - | (ZONE_NORMAL << __GFP_MOVABLE * ZONES_SHIFT) \
> > > - | (OPT_ZONE_DMA << (__GFP_MOVABLE | __GFP_DMA) * ZONES_SHIFT) \
> > > - | (ZONE_MOVABLE << (__GFP_MOVABLE | __GFP_HIGHMEM) * ZONES_SHIFT)\
> > > - | (OPT_ZONE_DMA32 << (__GFP_MOVABLE | __GFP_DMA32) * ZONES_SHIFT)\
> > > + (ZONE_NORMAL << ZT_SHIFT(0)) \
> > > + | (OPT_ZONE_DMA << ZT_SHIFT(__GFP_DMA)) \
> > > + | (OPT_ZONE_HIGHMEM << ZT_SHIFT(__GFP_HIGHMEM)) \
> > > + | (OPT_ZONE_DMA32 << ZT_SHIFT(__GFP_DMA32)) \
> > > + | (ZONE_NORMAL << ZT_SHIFT(__GFP_MOVABLE)) \
> > > + | (OPT_ZONE_DMA << ZT_SHIFT(__GFP_MOVABLE | __GFP_DMA)) \
> > > + | (ZONE_MOVABLE << ZT_SHIFT(__GFP_MOVABLE | __GFP_HIGHMEM)) \
> > > + | (OPT_ZONE_DMA32 << ZT_SHIFT(__GFP_MOVABLE | __GFP_DMA32)) \
> > > )
> >
> > hm. I hope these sparse warnings are sufficiently useful to justify
> > all the gunk we're adding to support them.
> >
> > Is it actually finding any bugs?
>
> FWIW, bitwise or done in the right-hand argumet of shift looks ugly as hell;
> what the hell is that code _doing_?
There's a nice fat comment a few lines up...
/*
* GFP_ZONE_TABLE is a word size bitstring that is used for looking up the
* zone to use given the lowest 4 bits of gfp_t. Entries are ZONE_SHIFT long
* and there are 16 of them to cover all possible combinations of
* __GFP_DMA, __GFP_DMA32, __GFP_MOVABLE and __GFP_HIGHMEM.
*
* The zone fallback order is MOVABLE=>HIGHMEM=>NORMAL=>DMA32=>DMA.
* But GFP_MOVABLE is not only a zone specifier but also an allocation
* policy. Therefore __GFP_MOVABLE plus another zone selector is valid.
* Only 1 bit of the lowest 3 bits (DMA,DMA32,HIGHMEM) can be set to "1".
*
* bit result
* =================
* 0x0 => NORMAL
* 0x1 => DMA or NORMAL
* 0x2 => HIGHMEM or NORMAL
* 0x3 => BAD (DMA+HIGHMEM)
* 0x4 => DMA32 or DMA or NORMAL
* 0x5 => BAD (DMA+DMA32)
* 0x6 => BAD (HIGHMEM+DMA32)
* 0x7 => BAD (HIGHMEM+DMA32+DMA)
* 0x8 => NORMAL (MOVABLE+0)
* 0x9 => DMA or NORMAL (MOVABLE+DMA)
* 0xa => MOVABLE (Movable is valid only if HIGHMEM is set too)
* 0xb => BAD (MOVABLE+HIGHMEM+DMA)
* 0xc => DMA32 (MOVABLE+HIGHMEM+DMA32)
* 0xd => BAD (MOVABLE+DMA32+DMA)
* 0xe => BAD (MOVABLE+DMA32+HIGHMEM)
* 0xf => BAD (MOVABLE+DMA32+HIGHMEM+DMA)
*
* ZONES_SHIFT must be <= 2 on 32 bit platforms.
*/
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next prev parent reply other threads:[~2010-09-28 21:45 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-09-28 12:23 [PATCH] mm: cleanup gfp_zone() Namhyung Kim
2010-09-28 21:32 ` Andrew Morton
2010-09-28 21:41 ` Al Viro
2010-09-28 21:45 ` Andrew Morton [this message]
2010-09-28 22:15 ` Al Viro
2010-09-29 7:06 ` [PATCH v2] mm: fix sparse warnings on GFP_ZONE_TABLE/BAD Namhyung Kim
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