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    SubjectRe: Better pagecache statistics ?
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    On Thu, 2005-12-01 at 15:57 -0200, Marcelo Tosatti wrote:
    > On Thu, Dec 01, 2005 at 06:21:39PM +0100, Arjan van de Ven wrote:
    > > On Thu, 2005-12-01 at 09:15 -0800, Badari Pulavarty wrote:
    > > > > Most of the issues you mention are null if you move the stats
    > > > > maintenance burden to userspace.
    > > > >
    > > > > The performance impact is also minimized since the hooks
    > > > > (read: overhead) can be loaded on-demand as needed.
    > > > >
    > > >
    > > > The overhead is - going through each mapping/inode in the system
    > > > and dumping out "nrpages" - to get per-file statistics. This is
    > > > going to be expensive, need locking and there is no single list
    > > > we can traverse to get it. I am not sure how to do this.
    >
    > Can't you add hooks to add_to_page_cache/remove_from_page_cache
    > to record pagecache activity ?

    In theory, yes. We already maintain info in "mapping->nrpages".
    Trick would be to collect all of them, send them to user space.

    Thanks,
    Badari

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