linux-kernel - Re: [PATCH v4 14/25] rmap: Add support for PUD sized mappings to rmap

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Message-ID: <107dacce-87dc-457b-a2e1-e5a4699d66af@redhat.com>
Date: Fri, 20 Dec 2024 19:31:03 +0100
From: David Hildenbrand <david@...hat.com>
To: Alistair Popple <apopple@...dia.com>
Cc: akpm@...ux-foundation.org, dan.j.williams@...el.com, linux-mm@...ck.org,
 lina@...hilina.net, zhang.lyra@...il.com, gerald.schaefer@...ux.ibm.com,
 vishal.l.verma@...el.com, dave.jiang@...el.com, logang@...tatee.com,
 bhelgaas@...gle.com, jack@...e.cz, jgg@...pe.ca, catalin.marinas@....com,
 will@...nel.org, mpe@...erman.id.au, npiggin@...il.com,
 dave.hansen@...ux.intel.com, ira.weiny@...el.com, willy@...radead.org,
 djwong@...nel.org, tytso@....edu, linmiaohe@...wei.com, peterx@...hat.com,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linuxppc-dev@...ts.ozlabs.org,
 nvdimm@...ts.linux.dev, linux-cxl@...r.kernel.org,
 linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
 linux-xfs@...r.kernel.org, jhubbard@...dia.com, hch@....de,
 david@...morbit.com
Subject: Re: [PATCH v4 14/25] rmap: Add support for PUD sized mappings to rmap

>>>    				return -EBUSY;
>>> diff --git a/mm/rmap.c b/mm/rmap.c
>>> index c6c4d4e..39d0439 100644
>>> --- a/mm/rmap.c
>>> +++ b/mm/rmap.c
>>> @@ -1203,6 +1203,11 @@ static __always_inline unsigned int __folio_add_rmap(struct folio *folio,
>>>    		}
>>>    		atomic_inc(&folio->_large_mapcount);
>>>    		break;
>>> +	case RMAP_LEVEL_PUD:
>>> +		/* We only support entire mappings of PUD sized folios in rmap */
>>> +		atomic_inc(&folio->_entire_mapcount);
>>> +		atomic_inc(&folio->_large_mapcount);
>>> +		break;
>>
>>
>> This way you don't account the pages at all as mapped, whereby PTE-mapping it
>> would? And IIRC, these PUD-sized pages can be either mapped using PTEs or
>> using a single PUD.
> 
> Oh good point. I was thinking that because we don't account PUD mappings today
> that it would be fine to ignore them. But of course this series means we start
> accounting them if mapped with PTEs so agree we should be consistent.
>   
>> I suspect what you want is to
> 
> Yes, I think so. Thanks for the hint. I will be out over the Christmas break but
> will do a respin to incorporate this before then.

I'll be on PTO starting ... well now. But I'll try to give the other 
parts a quick peek if anything urgent jumps at me. (bad habit of reading 
mails while on PTO ...)

In any case, happy holidays to you!

-- 
Cheers,

David / dhildenb