linux-kernel - Re: [PATCH 00/16] mm: prepare for converting vm->vm

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Date:	Thu, 22 Mar 2012 14:39:59 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
Cc:	Minchan Kim <minchan@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Ben Herrenschmidt <benh@...nel.crashing.org>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>
Subject: Re: [PATCH 00/16] mm: prepare for converting vm->vm_flags to 64-bit

On Wed, Mar 21, 2012 at 05:16:06PM +0400, Konstantin Khlebnikov wrote:
> Minchan Kim wrote:
> >Hi Konstantin,
> >
> >It seems to be nice clean up to me and you are a volunteer we have been wanted
> >for a long time. Thanks!
> >I am one of people who really want to expand vm_flags to 64 bit but when KOSAKI
> >tried it, Linus said his concerning, I guess you already saw that.
> >
> >He want to tidy vm_flags's usage up rather than expanding it.
> >Without the discussion about that, just expanding vm_flags would make us use
> >it up easily so that we might need more space.
> 
> Strictly speaking, my pachset does not expands vm_flags, it just prepares to this.
> Anyway vm_flags_t looks better than hard-coded "unsigned long" and messy type-casts around it.

Indeed.

> 
> >
> >Readahead flags are good candidate to move into another space and arch-specific flags, I guess.
> >Another candidate I think of is THP flag. It's just for only anonymous vma now
> >(But I am not sure we have a plan to support it for file-backed pages in future)
> >so we can move it to anon_vma or somewhere.
> >I think other guys might find more somethings
> >
> >The point is that at least, we have to discuss about clean up current vm_flags's
> >use cases before expanding it unconditionally.
> 
> Seems like we can easily remove VM_EXECUTABLE
> (count in mm->num_exe_file_vmas amount of vmas with vma->vm_file == mm->exe_file
> instead of vmas with VM_EXECUTABLE bit)
> 
> And probably VM_CAN_NONLINEAR...

I think we can also unify VM_MAPPED_COPY(nommu) and VM_SAO(powerpc) with one VM_ARCH_1
Okay. After this series is merged, let's try to remove flags we can do. Then, other guys
might suggest another ideas.

Thanks.
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