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    SubjectRe: 2.4.8/2.4.9 VM problems


    On Tue, 21 Aug 2001, Daniel Phillips wrote:

    > On August 20, 2001 10:16 pm, Marcelo Tosatti wrote:
    > > On Mon, 20 Aug 2001, Marcelo Tosatti wrote:
    > > > On Mon, 20 Aug 2001, Daniel Phillips wrote:
    > > > > On Mon, 20 Aug 2001, Marcelo Tosatti wrote:
    > > > > > Find riel's message with topic "VM tuning" to linux-mm, then take a look
    > > > > > at the 4th aging option.
    > > > > >
    > > > > > That one _should_ be able to make us remove all kinds of "hacks" to do
    > > > > > drop behind, and also it should keep hot/warm active memory _in cache_
    > > > > > for more time.
    > > > >
    > > > > I looked at it yesterday. The problem is, it loses the information about *how*
    > > > > a page is used: pagecache lookup via readahead has different implications than
    > > > > actual usage.
    > >
    > > And ah, I forgot something here.
    > >
    > > Your statement which says "pagecache lookup via readahead has different
    > > implications than actual usage" is not really correct.
    > >
    > > If you only consider "hot" pages as "pages which have been touched",
    > > you're going to (potentially) fuck heavy streaming IO workloads.
    >
    > "Hot" pages are pages that have been touched more than once.
    >
    > The idea of use-once (on the read side) is to retain the readahead
    > pages just long enough to use them, and not a lot longer.
    >
    > If you've seen streaming IO pages getting evicted before being used,
    > I'd like to know about it because something is broken in that case.

    I've seen the first page read by "swapin_readahead()" (which is the actual
    page we want to swapin) be evicted _before_ we could actually use it (so
    the read_swap_cache_async() call had to read the same page _again_ from
    disk).


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