Re: [RFC PATCH] mm/vmscan: Don't round up scan size for online memory cgroup

[Gavin Shan <gshan@redhat.com>]

On 2/11/20 2:03 PM, Yang Shi wrote:
> On Mon, Feb 10, 2020 at 6:18 PM Gavin Shan <gshan@redhat.com> wrote:
>> On 2/11/20 12:31 PM, Roman Gushchin wrote:
>>> On Tue, Feb 11, 2020 at 10:55:53AM +1100, Gavin Shan wrote:
>>>> On 2/11/20 3:17 AM, Roman Gushchin wrote:
>>>>> On Mon, Feb 10, 2020 at 11:14:45PM +1100, Gavin Shan wrote:

.../...

>>
>> There is something which might be unrelated to discuss here: the pagecache could be backed
>> by a low-speed (HDD) or high-speed (SSD) media. So the cost to fetch them from disk to memory
>> isn't equal, meaning we need some kind of bias during reclaiming. It seems something missed
>> from current implementation.
> 
> Yes, the refault cost was not taken into account. I recalled Johannes
> posted a patch series to do swap with refault cost weighted in a
> couple of years ago, please see: https://lwn.net/Articles/690079/.
> 

Thanks for the link. Yes, Johannes's patchset is comprehensive, even I
didn't look into the details. The concern I had is fixed bias to pagecaches
backed by different storage device, which have different IO speed. It seems
the patchset was disconnected since v1 because I didn't find a v2 from
google.

Thanks,
Gavin