linux-kernel - Re: [PATCH v1] drivers/base/node.c: Simplify unregister_memory_block_under

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Message-ID: <20190719113647.GS30461@dhcp22.suse.cz>
Date:   Fri, 19 Jul 2019 13:36:47 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Oscar Salvador <osalvador@...e.de>
Subject: Re: [PATCH v1] drivers/base/node.c: Simplify
 unregister_memory_block_under_nodes()

On Fri 19-07-19 11:20:43, David Hildenbrand wrote:
> On 19.07.19 11:13, Michal Hocko wrote:
> > On Fri 19-07-19 11:05:51, David Hildenbrand wrote:
> >> On 19.07.19 10:42, Michal Hocko wrote:
> >>> On Thu 18-07-19 16:22:39, David Hildenbrand wrote:
> >>>> We don't allow to offline memory block devices that belong to multiple
> >>>> numa nodes. Therefore, such devices can never get removed. It is
> >>>> sufficient to process a single node when removing the memory block.
> >>>>
> >>>> Remember for each memory block if it belongs to no, a single, or mixed
> >>>> nodes, so we can use that information to skip unregistering or print a
> >>>> warning (essentially a safety net to catch BUGs).
> >>>
> >>> I do not really like NUMA_NO_NODE - 1 thing. This is yet another invalid
> >>> node that is magic. Why should we even care? In other words why is this
> >>> patch an improvement?
> >>
> >> Oh, and to answer that part of the question:
> >>
> >> We no longer have to iterate over each pfn of a memory block to be removed.
> > 
> > Is it possible that we are overzealous when unregistering syfs files and
> > we should simply skip the pfn walk even without this change?
> > 
> 
> I assume you mean something like v1 without the warning/"NUMA_NO_NODE -1"?
> 
> See what I have right now below.

Yes. I didn'g get to look closely but you caught the idea. Thanks!
-- 
Michal Hocko
SUSE Labs