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

[Dave Hansen]

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().