Message-ID: <ebed9128-a56f-0493-0cc8-d13e1de077fc@redhat.com>
Date:   Wed, 8 Feb 2023 11:13:57 +0100
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Subject: Re: [RFC v3 2/4] mm: move PG_slab flag to page_type
To:     Mike Rapoport <rppt@kernel.org>
Cc:     Matthew Wilcox <willy@infradead.org>,
        Hyeonggon Yoo <42.hyeyoo@gmail.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        =?UTF-8?B?SE9SSUdVQ0hJIE5BT1lBKOWggOWPoyDnm7TkuZ8p?= 
        <naoya.horiguchi@nec.com>, Joe Perches <joe@perches.com>,
        Petr Mladek <pmladek@suse.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Alexander Potapenko <glider@google.com>,
        Marco Elver <elver@google.com>
References: <20221218101901.373450-1-42.hyeyoo@gmail.com>
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 <Y9dRlNhh6O99tg4E@casper.infradead.org>
 <59630801-42b4-22e8-0ef6-5a5b8636dfbd@redhat.com>
 <Y+NvCts0JPBmAifu@kernel.org>
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From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
In-Reply-To: <Y+NvCts0JPBmAifu@kernel.org>
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On 08.02.23 10:44, Mike Rapoport wrote:
> On Fri, Feb 03, 2023 at 05:04:01PM +0100, David Hildenbrand wrote:
>> On 30.01.23 06:11, Matthew Wilcox wrote:
>>> On Mon, Jan 30, 2023 at 01:34:59PM +0900, Hyeonggon Yoo wrote:
>>>>> Seems like quite some changes to page_type to accomodate SLAB, which is
>>>>> hopefully going away soon(TM). Could we perhaps avoid that?
>>>>
>>>> If it could be done with less changes, I'll try to avoid that.
>>>
>>> Let me outline the idea I had for removing PG_slab:
>>>
>>> Observe that PG_reserved and PG_slab are mutually exclusive.  Also,
>>
>> I recall that there are SetPageReserved() calls on pages allocated via slab.
> 
> I did a quick scan, and it seems that all allocated reserved pages come
> from alloc_pages() or vmalloc().
>   

Thanks for checking, good that my memory was wrong :)

> BTW, looking at the current usage of SetPageReserved, it seems that some
> are bogus/historical and some would justify a different page type if we are
> to have 15 bits for PG_kernel.

I remember raising in the past that something like PG_hole might be helpful.

I also recall that most SetPageReserved usage in drivers is to make 
ioremap happy. PG_ioremappable or smth like that would be better.

So yes, that would even help to cleanup the existing PG_reserved usage.

-- 
Thanks,

David / dhildenb