linux-ext4 - Re: [PATCH 02/12] pci/p2pdma: Don't initialise page refcount to one

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Message-ID: <87r09rgfjj.fsf@nvdebian.thelocal>
Date: Wed, 11 Sep 2024 11:07:51 +1000
From: Alistair Popple <apopple@...dia.com>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: dan.j.williams@...el.com, linux-mm@...ck.org, 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, david@...hat.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 02/12] pci/p2pdma: Don't initialise page refcount to one


>> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
>> index 4f47a13..210b9f4 100644
>> --- a/drivers/pci/p2pdma.c
>> +++ b/drivers/pci/p2pdma.c
>> @@ -129,6 +129,12 @@ static int p2pmem_alloc_mmap(struct file *filp, struct kobject *kobj,
>>  	}
>>  
>>  	/*
>> +	 * Initialise the refcount for the freshly allocated page. As we have
>> +	 * just allocated the page no one else should be using it.
>> +	 */
>> +	set_page_count(virt_to_page(kaddr), 1);
>
> No doubt the subject line is true in some overall context, but it does
> seem to say the opposite of what happens here.

Fair. It made sense to me from the mm context I was coming from (it was
being initialised to 1 there) but not overall. Something like "move page
refcount initialisation to p2pdma driver" would make more sense?

 - Alistair

> Bjorn