linux-kernel - Re: [PATCH v2 3/7] x86, gfp: Cache best near node for memory allocation.

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Date:	Thu, 10 Sep 2015 15:38:19 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Tang Chen <tangchen@...fujitsu.com>
Cc:	jiang.liu@...ux.intel.com, mika.j.penttila@...il.com,
	mingo@...hat.com, akpm@...ux-foundation.org, rjw@...ysocki.net,
	hpa@...or.com, yasu.isimatu@...il.com,
	isimatu.yasuaki@...fujitsu.com, kamezawa.hiroyu@...fujitsu.com,
	izumi.taku@...fujitsu.com, gongzhaogang@...pur.com,
	qiaonuohan@...fujitsu.com, x86@...nel.org,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Gu Zheng <guz.fnst@...fujitsu.com>,
	Christoph Lameter <cl@...ux-foundation.org>
Subject: Re: [PATCH v2 3/7] x86, gfp: Cache best near node for memory
 allocation.

(cc'ing Christoph Lameter)

On Thu, Sep 10, 2015 at 03:29:35PM -0400, Tejun Heo wrote:
> Hello,
> 
> On Thu, Sep 10, 2015 at 12:27:45PM +0800, Tang Chen wrote:
> > diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> > index ad35f30..1a1324f 100644
> > --- a/include/linux/gfp.h
> > +++ b/include/linux/gfp.h
> > @@ -307,13 +307,19 @@ static inline struct page *alloc_pages_node(int nid, gfp_t gfp_mask,
> >  	if (nid < 0)
> >  		nid = numa_node_id();
> >  
> > +	if (!node_online(nid))
> > +		nid = get_near_online_node(nid);
> > +
> >  	return __alloc_pages(gfp_mask, order, node_zonelist(nid, gfp_mask));
> >  }
> 
> Why not just update node_data[]->node_zonelist in the first place?
> Also, what's the synchronization rule here?  How are allocators
> synchronized against node hot [un]plugs?

Also, shouldn't kmalloc_node() or any public allocator fall back
automatically to a near node w/o GFP_THISNODE?  Why is this failing at
all?  I get that cpu id -> node id mapping changing messes up the
locality but allocations shouldn't fail, right?

Thanks.

-- 
tejun
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