On 08/01/2025 04:56, Andrew Morton wrote:
> On Tue, 7 Jan 2025 14:25:53 +0000 Ryan Roberts <ryan.roberts@xxxxxxx> wrote:
>
>> After commit b1f202060afe ("mm: remap unused subpages to shared zeropage
>> when splitting isolated thp"), cow test cases involving swapping out
>> THPs via madvise(MADV_PAGEOUT) started to be skipped due to the
>> subsequent check via pagemap determining that the memory was not
>> actually swapped out. Logs similar to this were emitted:
>>
>> ...
>>
>> The commit in question introduces the behaviour of scanning THPs and if
>> their content is predominantly zero, it splits them and replaces the
>> pages which are wholly zero with the zero page. These cow test cases
>> were getting caught up in this.
>>
>> So let's avoid that by filling the contents of all allocated memory with
>> a non-zero value. With this in place, the tests are passing again.
>>
>
> Thanks, I'll add
>
> Fixes: b1f202060afe ("mm: remap unused subpages to shared zeropage when splitting isolated thp")
Thanks, given it's not really a bug but a deliberate change of behaviour I
wasn't sure that a Fixes tag was appropriate, but thanks for seting me straight.
> ...
> Cc: Usama Arif <usamaarif642@xxxxxxxxx>
> Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>
