linux-kernel - Re: [PATCH v2 1/2] mm/vmalloc: fix numa spreading for large hash tables

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Date:   Tue, 19 Oct 2021 08:58:48 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Chen Wandun <chenwandun@...wei.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Kefeng Wang <wangkefeng.wang@...wei.com>, guohanjun@...wei.com,
        "Uladzislau Rezki (Sony)" <urezki@...il.com>
Subject: Re: [PATCH v2 1/2] mm/vmalloc: fix numa spreading for large hash tables

On Tue, Oct 19, 2021 at 8:54 AM Shakeel Butt <shakeelb@...gle.com> wrote:
>
> On Mon, Oct 18, 2021 at 5:41 AM Matthew Wilcox <willy@...radead.org> wrote:
> >
> > On Mon, Oct 18, 2021 at 08:37:09PM +0800, Chen Wandun wrote:
> > > Eric Dumazet reported a strange numa spreading info in [1], and found
> > > commit 121e6f3258fe ("mm/vmalloc: hugepage vmalloc mappings") introduced
> > > this issue [2].
> >
> > I think the root problem here is that we have two meanings for
> > NUMA_NO_NODE.  I tend to read it as "The memory can be allocated from
> > any node", but here it's used to mean "The memory should be spread over
> > every node".  Should we split those out as -1 and -2?
>
> I agree with Willy's suggestion to make it more explicit but as a
> followup work. This patch needs a backport, so keep this simple.

NUMA_NO_NODE in process context also meant :
Please follow current thread NUMA policies.

One could hope for instance, that whenever large BPF maps are allocated,
current thread could set non default NUMA policies.