linux-kernel - Re: [RFC PATCH 0/3] Interface for higher order contiguous allocations

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Message-ID: <770445b3-6caa-a87a-5de7-3157fc5280c2@intel.com>
Date:   Thu, 15 Feb 2018 12:22:33 -0800
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Cc:     Michal Hocko <mhocko@...nel.org>,
        Christopher Lameter <cl@...ux.com>,
        Guy Shattah <sguy@...lanox.com>,
        Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
        Michal Nazarewicz <mina86@...a86.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        David Nellans <dnellans@...dia.com>,
        Laura Abbott <labbott@...hat.com>, Pavel Machek <pavel@....cz>,
        Dave Hansen <dave.hansen@...el.com>
Subject: Re: [RFC PATCH 0/3] Interface for higher order contiguous allocations

Hi Mike,

On 2/12/2018 2:20 PM, Mike Kravetz wrote:
> These patches came out of the "[RFC] mmap(MAP_CONTIG)" discussions at:
> http://lkml.kernel.org/r/21f1ec96-2822-1189-1c95-79a2bb491571@oracle.com
> 
> One suggestion in that thread was to create a friendlier interface that
> could be used by drivers and others outside core mm code to allocate a
> contiguous set of pages.  The alloc_contig_range() interface is used for
> this purpose today by CMA and gigantic page allocation.  However, this is
> not a general purpose interface.  So, wrap alloc_contig_range() in the
> more general interface:
> 
> struct page *find_alloc_contig_pages(unsigned int order, gfp_t gfp, int nid,
> 					nodemask_t *nodemask)
> 
> No underlying changes are made to increase the likelihood that a contiguous
> set of pages can be found and allocated.  Therefore, any user of this
> interface must deal with failure.  The hope is that this interface will be
> able to satisfy some use cases today.

As discussed in another thread a new feature, Cache Pseudo-Locking,
requires large contiguous regions. Until now I just exposed
alloc_gigantic_page() to handle these allocations in my testing. I now
moved to using find_alloc_contig_pages() as introduced here and all my
tests passed. I do hope that an API supporting large contiguous regions
become available.

Thank you very much for creating this.

Tested-by: Reinette Chatre <reinette.chatre@...el.com>

Reinette