linux-kernel - Re: [PATCH v1 1/1] fs/splice: add missing callback for inaccessible pages

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Date:   Thu, 30 Apr 2020 21:02:21 +0200
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Dave Hansen <dave.hansen@...el.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        akpm@...ux-foundation.org, jack@...e.cz, kirill@...temov.name
Cc:     david@...hat.com, aarcange@...hat.com, linux-mm@...ck.org,
        frankja@...ux.ibm.com, sfr@...b.auug.org.au, jhubbard@...dia.com,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        peterz@...radead.org, sean.j.christopherson@...el.com,
        Ulrich Weigand <Ulrich.Weigand@...ibm.com>
Subject: Re: [PATCH v1 1/1] fs/splice: add missing callback for inaccessible
 pages

On 30.04.20 20:12, Christian Borntraeger wrote:
> 
> 
> On 29.04.20 18:07, Dave Hansen wrote:
>> On 4/28/20 3:50 PM, Claudio Imbrenda wrote:
>>> If a page is inaccesible and it is used for things like sendfile, then
>>> the content of the page is not always touched, and can be passed
>>> directly to a driver, causing issues.
>>>
>>> This patch fixes the issue by adding a call to arch_make_page_accessible
>>> in page_cache_pipe_buf_confirm; this fixes the issue.
>>
>> I spent about 5 minutes putting together a patch:
>>
>> 	https://sr71.net/~dave/intel/accessible.patch
> 
> You only set the page flag for compound pages. that of course leaves a big pile
> of pages marked a not accessible, thus explaining the sendto trace and all kind
> of other random traces.
> 
> 
> What do you see when you also do the  SetPageAccessible(page);
> in the else page of prep_new_page (order == 0).
> (I do get > 10000 of these non compound page allocs just during boot).
> 

And yes, I think you are right that we should call the callback also for !FOLL_PIN.