linux-kernel - Re: [PATCH v2 3/4] mm: add find_alloc_contig

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Message-ID: <01793788-1870-858e-2061-a0e6ef3a3171@suse.cz>
Date:   Wed, 23 May 2018 13:18:10 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Reinette Chatre <reinette.chatre@...el.com>,
        Mike Kravetz <mike.kravetz@...cle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-api@...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>,
        David Nellans <dnellans@...dia.com>,
        Laura Abbott <labbott@...hat.com>, Pavel Machek <pavel@....cz>,
        Dave Hansen <dave.hansen@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2 3/4] mm: add find_alloc_contig_pages() interface

On 05/22/2018 06:41 PM, Reinette Chatre wrote:
> On 5/21/2018 4:48 PM, Mike Kravetz wrote:
>> I'm guessing that most (?all?) allocations will be order based.  The use
>> cases I am aware of (hugetlbfs, Intel Cache Pseudo-Locking, RDMA) are all
>> order based.  However, as commented in previous version taking arbitrary
>> nr_pages makes interface more future proof.
>>
> 
> I noticed this Cache Pseudo-Locking statement and would like to clarify.
> I have not been following this thread in detail so I would like to
> apologize first if my comments are out of context.
> 
> Currently the Cache Pseudo-Locking allocations are order based because I
> assumed it was required by the allocator. The contiguous regions needed
> by Cache Pseudo-Locking will not always be order based - instead it is
> based on the granularity of the cache allocation. One example is a
> platform with 55MB L3 cache that can be divided into 20 equal portions.
> To support Cache Pseudo-Locking on this platform we need to be able to
> allocate contiguous regions at increments of 2816KB (the size of each
> portion). In support of this example platform regions needed would thus
> be 2816KB, 5632KB, 8448KB, etc.

Will there be any alignment requirements for these allocations e.g. for
minimizing conflict misses?

Vlastimil