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

Christian Borntraeger
2020-04-30T19:45:39Z

On 30.04.20 21:32, Dave Hansen wrote:
> On 4/30/20 11:12 AM, 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.
>
> Ahh, nice catch! That does explain an oddity or two that I saw.
>
>> 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).
>
> Yes, I see the same thing.
>
> I updated the patch and double-checked that it triggers properly with a
> socket-based sendfile().

Can you place the updated patch somewhere?