linux-kernel - Re: + mm-revert-thp-make-madv_hugepage-check-for-mm-def

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Message-Id: <20140226152236.0757FE0098@blue.fi.intel.com>
Date:	Wed, 26 Feb 2014 17:22:35 +0200 (EET)
From:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:	Christian Borntraeger <borntraeger@...ibm.com>
Cc:	Oleg Nesterov <oleg@...hat.com>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, viro@...iv.linux.org.uk,
	schwidefsky@...ibm.com, rientjes@...gle.com, riel@...hat.com,
	peterz@...radead.org, pbonzini@...hat.com, mingo@...nel.org,
	mgorman@...e.de, kirill.shutemov@...ux.intel.com,
	heiko.carstens@...ibm.com, hannes@...xchg.org,
	gerald.schaefer@...ibm.com, ebiederm@...ssion.com,
	aarcange@...hat.com, athorlton@....com
Subject: Re: + mm-revert-thp-make-madv_hugepage-check-for-mm-def_flags.patch
 added to -mm tree

Christian Borntraeger wrote:
> On 26/02/14 15:50, Oleg Nesterov wrote:
> [...]
> 
> >> NAK.
> >>
> >> Since 2012 qemu does call "qemu_madvise(new_block->host, size, QEMU_MADV_HUGEPAGE);" for all kvm pages.
> >> (commit ad0b5321f1f797274603ebbe20108b0750baee94 Call MADV_HUGEPAGE for guest RAM allocations) so this
> >> breaks any recent kvm guest on s390.
> > 
> > Well, I can't really discuss the changes in arch/s390.
> > 
> > But perhaps qemu can be changed to avoid MADV_HUGEPAGE on s390 ?
> > Otherwise I'd suggest the change below.
> > 
> > Oleg.
> > 
> > 
> > --- x/mm/huge_memory.c
> > +++ x/mm/huge_memory.c
> > @@ -1968,8 +1968,6 @@ out:
> >  int hugepage_madvise(struct vm_area_struct *vma,
> >  		     unsigned long *vm_flags, int advice)
> >  {
> > -	struct mm_struct *mm = vma->vm_mm;
> > -
> >  	switch (advice) {
> >  	case MADV_HUGEPAGE:
> >  		/*
> > @@ -1977,8 +1975,16 @@ int hugepage_madvise(struct vm_area_stru
> >  		 */
> >  		if (*vm_flags & (VM_HUGEPAGE | VM_NO_THP))
> >  			return -EINVAL;
> > -		if (mm->def_flags & VM_NOHUGEPAGE)
> > +
> > +/*
> > + * MADV_HUGEPAGE after PRCTL_THP_DISABLE is broken on s390 because
> > + * qemu blindly does madvise(MADV_HUGEPAGE) after s390_enable_sie().
> > + */
> > +#ifdef CONFIG_S390
> > +		if (vma->vm_mm->def_flags & VM_NOHUGEPAGE)
> >  			return -EINVAL;
> > +#endif
> > +
> 
> Ifdefs are ugly

IS_ENABLED(CONFIG_S390) should help with this.

-- 
 Kirill A. Shutemov
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