linux-kernel - Re: No more bits in vm_area_struct's vm

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Message-Id: <20090925174009.79778649.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 25 Sep 2009 17:40:09 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Nigel Cunningham <ncunningham@...a.org.au>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: No more bits in vm_area_struct's vm_flags.

On Fri, 25 Sep 2009 18:34:56 +1000
Nigel Cunningham <ncunningham@...a.org.au> wrote:

> Hi.
> 
> KAMEZAWA Hiroyuki wrote:
> >> I have some code in TuxOnIce that needs a bit too (explicitly mark the
> >> VMA as needing to be atomically copied, for GEM objects), and am not
> >> sure what the canonical way to proceed is. Should a new unsigned long be
> >> added? The difficulty I see with that is that my flag was used in
> >> shmem_file_setup's flags parameter (drm_gem_object_alloc), so that
> >> function would need an extra parameter too..
> > 
> > Hmm, how about adding vma->vm_flags2 ?
> 
> The difficulty there is that some functions pass these flags as arguments.
> 
Ah yes. But I wonder some special flags, which is rarey used, can be moved
to vm_flags2...

For example,

 #define VM_SEQ_READ     0x00008000      /* App will access data sequentially */
 #define VM_RAND_READ    0x00010000      /* App will not benefit from clustered reads */
are all capsuled under
mm.h
 117 #define VM_READHINTMASK                 (VM_SEQ_READ | VM_RAND_READ)
 118 #define VM_ClearReadHint(v)             (v)->vm_flags &= ~VM_READHINTMASK
 119 #define VM_NormalReadHint(v)            (!((v)->vm_flags & VM_READHINTMASK))
 120 #define VM_SequentialReadHint(v)        ((v)->vm_flags & VM_SEQ_READ)
 121 #define VM_RandomReadHint(v)            ((v)->vm_flags & VM_RAND_READ)

Or

105 #define VM_PFN_AT_MMAP  0x40000000      /* PFNMAP vma that is fully mapped at mmap time */
is only used under special situation.

etc..

They'll be able to be moved to other(new) flag field, IIUC.

Thanks,
-Kame




> Regards,
> 
> Nigel
> 
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