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Date:   Mon, 25 Sep 2023 23:10:48 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Hugh Dickins <hughd@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Andi Kleen <ak@linux.intel.com>,
        Christoph Lameter <cl@linux.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        David Hildenbrand <david@redhat.com>,
        Suren Baghdasaryan <surenb@google.com>,
        Yang Shi <shy828301@gmail.com>,
        Sidhartha Kumar <sidhartha.kumar@oracle.com>,
        Vishal Moola <vishal.moola@gmail.com>,
        Kefeng Wang <wangkefeng.wang@huawei.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Tejun Heo <tj@kernel.org>,
        Mel Gorman <mgorman@techsingularity.net>,
        Michal Hocko <mhocko@suse.com>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [PATCH 02/12] kernfs: drop shared NUMA mempolicy hooks
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On Mon, Sep 25, 2023 at 01:22:27AM -0700, Hugh Dickins wrote:
> It seems strange that kernfs should be an outlier with a set_policy and
> get_policy in its kernfs_vm_ops.  Ah, it dates back to v2.6.30's commit
> 095160aee954 ("sysfs: fix some bin_vm_ops errors"), when I had crashed
> on powerpc's pci_mmap_legacy_page_range() fallback to shmem_zero_setup().
> 
> Well, that was commendably thorough, to give sysfs-bin a set_policy and
> get_policy, just to avoid the way it was coded resulting in EINVAL from
> mmap when CONFIG_NUMA; but somehow feels a bit over-the-top to me now.
> 
> It's easier to say that nobody should expect to manage a shmem object's
> shared NUMA mempolicy via some kernfs backdoor to that object: delete
> that code (and there's no longer an EINVAL from mmap in the NUMA case).
> 
> This then leaves set_policy/get_policy as implemented only by shmem -
> though importantly also by SysV SHM, which has to interface with shmem
> which implements them, and with SHM_HUGETLB which does not.
> 
> Signed-off-by: Hugh Dickins <hughd@google.com>

Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>