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

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Date:	Thu, 27 Feb 2014 17:45:24 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Gerald Schaefer <gerald.schaefer@...ibm.com>
Cc:	Alex Thorlton <athorlton@....com>,
	Peter Zijlstra <peterz@...radead.org>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	viro@...iv.linux.org.uk, schwidefsky@...ibm.com,
	rientjes@...gle.com, riel@...hat.com, pbonzini@...hat.com,
	mingo@...nel.org, mgorman@...e.de, kirill.shutemov@...ux.intel.com,
	heiko.carstens@...ibm.com, hannes@...xchg.org,
	ebiederm@...ssion.com, aarcange@...hat.com
Subject: Re: + mm-revert-thp-make-madv_hugepage-check-for-mm-def_flags.patch
	added to -mm tree

On 02/26, Gerald Schaefer wrote:
>
> On Wed, 26 Feb 2014 19:06:03 +0100
> Oleg Nesterov <oleg@...hat.com> wrote:
>
> > It would be nice to also change thp_split_mm() to not not play with
> > mm->def_flags, but I am not sure if we can do this.
>
> Hmm, I'm also wondering about this. Basically, we only need VM_NOHUGEPAGE
> in vma->vm_flags, which is done for all existing vmas in thp_split_mm().
> But if there should be new vmas created afterwards, it would still be
> necessary to also have VM_NOHUGEPAGE in mm->def_flags, because the
> vm_flags for new vmas will be set via OR of mm->def_flags, e.g. in
> do_brk() and do_mmap_pgoff().

Yes, exactly, this was my concern.

And while I know nothing about s390, it seems to me that huge pages should
be forbidden for any vma if ->has_pgste was set.

> Anyway, this would then have to be a separate patch, to keep the
> "revertability" of this hack.

Agreed. Thanks!

Oleg.

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