linux-kernel - Re: [PATCH V4] mm/thp: Allocate transparent hugepages on local node

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Message-ID: <20150126121309.GD25833@node.dhcp.inet.fi>
Date:	Mon, 26 Jan 2015 14:13:09 +0200
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Vlastimil Babka <vbabka@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	David Rientjes <rientjes@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH V4] mm/thp: Allocate transparent hugepages on local node

On Mon, Jan 26, 2015 at 12:41:55PM +0100, Vlastimil Babka wrote:
> On 01/21/2015 01:48 AM, Andrew Morton wrote:
> > On Tue, 20 Jan 2015 17:04:31 +0530 "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com> wrote:
> >> + * Should be called with the mm_sem of the vma hold.
> > 
> > That's a pretty cruddy sentence, isn't it?  Copied from
> > alloc_pages_vma().  "vma->vm_mm->mmap_sem" would be better.
> > 
> > And it should tell us whether mmap_sem required a down_read or a
> > down_write.  What purpose is it serving?
> 
> This is already said for mmap_sem further above this comment line, which
> should be just deleted (and from alloc_hugepage_vma comment too).
> 
> >> + *
> >> + */
> >> +struct page *alloc_hugepage_vma(gfp_t gfp, struct vm_area_struct *vma,
> >> +				unsigned long addr, int order)
> > 
> > This pointlessly bloats the kernel if CONFIG_TRANSPARENT_HUGEPAGE=n?
> > 
> > 
> > 
> > --- a/mm/mempolicy.c~mm-thp-allocate-transparent-hugepages-on-local-node-fix
> > +++ a/mm/mempolicy.c
> 
> How about this cleanup on top? I'm not fully decided on the GFP_TRANSHUGE test.
> This is potentially false positive, although I doubt anything else uses the same
> gfp mask bits.

This info on gfp mask should be in commit message.

And what about WARN_ON_ONCE() if we the matching bits with
!TRANSPARENT_HUGEPAGE?

> 
> Should "hugepage" be extra bool parameter instead? Should I #ifdef the parameter
> only for CONFIG_TRANSPARENT_HUGEPAGE, or is it not worth the ugliness?

Do we have spare gfp bit? ;)

-- 
 Kirill A. Shutemov
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