linux-kernel - Re: [PATCH, RFC, v2] shmat: introduce flag SHM_MAP

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Date:	Tue, 7 Oct 2008 13:09:00 +0300
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Ingo Molnar <mingo@...hat.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH, RFC, v2] shmat: introduce flag SHM_MAP_HINT

On Tue, Oct 07, 2008 at 10:20:30AM +0200, Andi Kleen wrote:
> On Tue, Oct 07, 2008 at 09:57:50AM +0300, Kirill A. Shutemov wrote:
> > It allows interpret attach address as a hint, not as exact address.
> 
> Please expand the description a bit. Rationale. etc.
> 
> > @@ -55,6 +55,7 @@ struct shmid_ds {
> >  #define	SHM_RND		020000	/* round attach address to SHMLBA boundary */
> >  #define	SHM_REMAP	040000	/* take-over region on attach */
> >  #define	SHM_EXEC	0100000	/* execution access */
> > +#define	SHM_MAP_HINT	0200000	/* interpret attach address as a hint */
> 
> search hint

Ok.

> > @@ -892,7 +892,7 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr)
> >  	sfd->vm_ops = NULL;
> >  
> >  	down_write(&current->mm->mmap_sem);
> > -	if (addr && !(shmflg & SHM_REMAP)) {
> > +	if (addr && !(shmflg & (SHM_REMAP|SHM_MAP_HINT))) {
> 
> I think you were right earlier that it can be just deleted, so why don't
> you just do that?

I want say that we shouldn't do this check if shmaddr is a search hint.
I'm not sure that check is unneeded if shmadd is the exact address.

-- 
Regards,  Kirill A. Shutemov
 + Belarus, Minsk
 + ALT Linux Team, http://www.altlinux.com/

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