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    SubjectRe: [PATCH] mm, swap: Make VMA based swap readahead configurable
    On Wed 27-09-17 14:04:01, Minchan Kim wrote:
    > On Tue, Sep 26, 2017 at 03:21:29PM +0200, Michal Hocko wrote:
    > > On Thu 21-09-17 09:33:10, Huang, Ying wrote:
    > > > From: Huang Ying <ying.huang@intel.com>
    > > >
    > > > This patch adds a new Kconfig option VMA_SWAP_READAHEAD and wraps VMA
    > > > based swap readahead code inside #ifdef CONFIG_VMA_SWAP_READAHEAD/#endif.
    > > > This is more friendly for tiny kernels.
    > >
    > > How (much)?
    > >
    > > > And as pointed to by Minchan
    > > > Kim, give people who want to disable the swap readahead an opportunity
    > > > to notice the changes to the swap readahead algorithm and the
    > > > corresponding knobs.
    > >
    > > Why would anyone want that?
    > >
    > > Please note that adding new config options make the already complicated
    > > config space even more problematic so there should be a good reason to
    > > add one. Please make sure your justification is clear on why this is
    > > worth the future maintenance and configurability burden.
    >
    > The problem is users have disabled swap readahead by echo 0 > /proc/sys/
    > vm/page-cluster are regressed by this new interface /sys/kernel/mm/swap/
    > vma_ra_max_order. Because for disabling readahead completely, they should
    > disable vma_ra_max_order as well as page-cluster from now on.
    >
    > So, goal of new config to notice new feature to admins so they can be aware
    > of new konb vma_ra_max_order as well as page-cluster.
    > I canont think other better idea to preventing such regression.
    >
    > http://lkml.kernel.org/r/%3C20170913014019.GB29422@bbox%3E

    So, how are you going to configure this when you do not know whether
    zram will be used? In other words what should e.g. distribution set this
    to?

    --
    Michal Hocko
    SUSE Labs

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