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    SubjectRe: [2.4] heavy-load under swap space shortage
    Marcelo Tosatti <marcelo.tosatti@cyclades.com> wrote:
    >
    > At first I was skeptic to the inclusion of this patch in v2.4 (due to the
    > freeze), but after thinking a bit more about I have a few points in favour
    > of this modification (read Nomura's message below and the patch to know
    > what I'm talking about):
    >
    > - It is off by default
    > - It is very simple (non intrusive), it just changes the point in which
    > anonymous pages are inserted into the LRU.
    > - When turned on, I dont see it being a reason for introducing new
    > bugs.
    >
    > What you think of this?

    hm, I hadn't noticed that 2.4 was changed to _not_ add anon pages to the
    LRU. I'd always regarded that as a workaround for pagemap_lru_lock contention
    on large SMP machines which would never get beyond the suse kernel.

    Having a magic knob is a weak solution: the majority of people who are
    affected by this problem won't know to turn it on.

    I confess that I don't really understand the failure mode. So we have
    zillions of anon pages which are not on the LRU. We call swap_out() and
    scan all these pages, failing to find swapcache space for them.

    Why does adding the pages to the LRU up-front solve the problem?

    (And why cannot we lazily add these anon pages to the LRU in swap_out, and
    avoid the need for the knob?)

    -
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