Re: [PATCH v3 0/3] free reclaimed pages by paging out instantly

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 3 Jul 2014 09:59:49 +0900 Minchan Kim <minchan@kernel.org> wrote:

> > > Most of field in vmstat are not changed too much but things I can notice
> > > is allocstall and pgrotated. We could save allocstall(ie, direct relcaim)
> > > and pgrotated very much.
> > > 
> > > Welcome testing, review and any feedback!
> > 
> > Well, it will worsen IRQ latencies and it's all more code for us to
> > maintain.  I think I'd like to see a better story about the end-user
> > benefits before proceeding.
> 
> The motivation was from per-process reclaim(which was internal feature
> yet and and I will repost it soon).
> It's a feature for us to manage memory from platform so that we could
> avoid reclaim.
> 
> Anyway, userspace expect they could see increased free pages in vmstat
> after they have done per-process reclaim so the logic of userspace
> will control their next action depending on the number of current
> free page but it doesn't work with existing rotation logic, expecially
> anon swap write pages.
> 
> When I posted this patchset firstly, Rik was positive and I thought
> this feature is useful for everyone as well as per-process reclaim
> and don't want to make noise this patchset with perpcoess reclaim.
> 
> https://lkml.org/lkml/2013/5/12/174
> https://lkml.org/lkml/2013/5/14/484
> 
> Could you tell me what should I do to proceed?

Quantify the gains, quantify the losses then demonstrate that the
benefits of the gains exceeds the cost of the losses plus the cost of
ongoing maintenance!