linux-kernel - Re: [PATCH] mm: rename and document alloc_pages_exact

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Message-ID: <alpine.DEB.2.10.1507211428160.3833@chino.kir.corp.google.com>
Date:	Tue, 21 Jul 2015 14:31:09 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Vlastimil Babka <vbabka@...e.cz>
cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-ia64@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	cbe-oss-dev@...ts.ozlabs.org, kvm@...r.kernel.org,
	Mel Gorman <mgorman@...e.de>, Greg Thelen <gthelen@...gle.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Tony Luck <tony.luck@...el.com>,
	Fenghua Yu <fenghua.yu@...el.com>,
	Arnd Bergmann <arnd@...db.de>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Gleb Natapov <gleb@...nel.org>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Cliff Whickman <cpw@....com>,
	Robin Holt <robinmholt@...il.com>
Subject: Re: [PATCH] mm: rename and document alloc_pages_exact_node

On Tue, 21 Jul 2015, Vlastimil Babka wrote:

> The function alloc_pages_exact_node() was introduced in 6484eb3e2a81 ("page
> allocator: do not check NUMA node ID when the caller knows the node is valid")
> as an optimized variant of alloc_pages_node(), that doesn't allow the node id
> to be -1. Unfortunately the name of the function can easily suggest that the
> allocation is restricted to the given node. In truth, the node is only
> preferred, unless __GFP_THISNODE is among the gfp flags.
> 
> The misleading name has lead to mistakes in the past, see 5265047ac301 ("mm,
> thp: really limit transparent hugepage allocation to local node") and
> b360edb43f8e ("mm, mempolicy: migrate_to_node should only migrate to node").
> 
> To prevent further mistakes, this patch renames the function to
> alloc_pages_prefer_node() and documents it together with alloc_pages_node().
> 

alloc_pages_exact_node(), as you said, connotates that the allocation will 
take place on that node or will fail.  So why not go beyond this patch and 
actually make alloc_pages_exact_node() set __GFP_THISNODE and then call 
into a new alloc_pages_prefer_node(), which would be the current 
alloc_pages_exact_node() implementation, and then fix up the callers?
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