linux-kernel - Re: [PATCH 0/6] make memblock allocator utilize the node's fallback info

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Date:   Tue, 26 Feb 2019 13:09:19 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Pingfan Liu <kernelfans@...il.com>
Cc:     x86@...nel.org, linux-mm@...ck.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andy Lutomirski <luto@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Petr Tesarik <ptesarik@...e.cz>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Jonathan Corbet <corbet@....net>,
        Nicholas Piggin <npiggin@...il.com>,
        Daniel Vacek <neelx@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/6] make memblock allocator utilize the node's fallback
 info

On Tue 26-02-19 13:47:37, Pingfan Liu wrote:
> On Tue, Feb 26, 2019 at 12:04 AM Michal Hocko <mhocko@...nel.org> wrote:
> >
> > On Sun 24-02-19 20:34:03, Pingfan Liu wrote:
> > > There are NUMA machines with memory-less node. At present page allocator builds the
> > > full fallback info by build_zonelists(). But memblock allocator does not utilize
> > > this info. And for memory-less node, memblock allocator just falls back "node 0",
> > > without utilizing the nearest node. Unfortunately, the percpu section is allocated
> > > by memblock, which is accessed frequently after bootup.
> > >
> > > This series aims to improve the performance of per cpu section on memory-less node
> > > by feeding node's fallback info to memblock allocator on x86, like we do for page
> > > allocator. On other archs, it requires independent effort to setup node to cpumask
> > > map ahead.
> >
> > Do you have any numbers to tell us how much does this improve the
> > situation?
> 
> Not yet. At present just based on the fact that we prefer to allocate
> per cpu area on local node.

Yes, we _usually_ do. But the additional complexity should be worth it.
And if we find out that the final improvement is not all that great and
considering that memory-less setups are crippled anyway then it might
turn out we just do not care all that much.
-- 
Michal Hocko
SUSE Labs